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ULNA. One of the two bones of the forearm. It forms the hinge joint at the elbow and does not rotate about its longitudinal axis. It terminates at the wrist on the same side as the little finger. Task design should not impose thrust loads through the ulna.
ULNAR DEVIATION. A position of the hand in which the wrist is bent toward the little finger. Ulnar deviation is a poor working position for the hand and causes nerve and tendon damage. It reduces the useful range of pronation and supination (q.v.) by approximately 50 percent, and work performed in ulnar deviation proceeds at low efficiency. Hand tool design should avoid ulnar deviation.
ULNAR NERVE. One of three large nerves of the hand. It supplies muscles of fine manipulation (q.v.) located in the hand and provides sensory feedback (q.v.) via the skin of the little finger and part of the ring finger. Because the ulnar nerve enters the hand immediately below the skin, it is susceptible to damage from poorly designed tool handles which apply pressure to the palm on the side of the little finger.
ULTRASONICS. The use of high frequency vibrations for cleaning, heating tissues, dispersing solid mass, and imaging objects by reflection (1) Ultrasonic Cleaning The use of high frequency vibrations in a solvent bath to loosen and disperse surface contaminants. Typical frequencies for this application are 20-50 kHz. Also used in dentistry to remove deposits from tooth structure. (2) Ultrasonic Therapy The use of high frequency mechanical vibrations to transmit energy into and through body tissue to heat or disperse material. Typical frequency for this application is about one MHz. Ultrasonic phacoemulsification for removal of eye cataracts. Ultrasonic disintegration for pulverization of bladder calculi. (3) Ultrasonic Imaging The use of high frequency vibrations to obtain a visual image of internal organs and soft tissue, most often using pulse echo techniques. Typical frequencies for this application are 1-15 MHz. Examples are echocardiology and echoencephalography.
ULTRASONIC TRANSDUCER. A device to convert electrical energy to mechanical energy, using piezo-electric materials such as quartz, barium titanate or lead metaniobate.
UNIVOCAL. Having a unique association. A relationship wherein one single specific effect can only be produced by one single specific cause, e.g., an ulnar claw can be produced only by damage to the ulnar nerve (q.v.).
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