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Index (U)

UA - UC

UD - UF

UG - UJ

UK - UN

UO - UR

US - UV

UW - UZ

Moment of truth
The fastest man-made object that ever leave the Earth is the New Horizon spacecraft, launched in January 2006, and attained a speed of more than 36000 mph.


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ultra-high frequency Elec.
The frequency range between 3 x 108 Hz and 3 x 109 Hz (corresponding wavelength of 10 to 100 cm. Abbreviated as UHF for television and radio transmission.

unavailable energy Phys.
The energy that no longer can be utilized to do spontaneous work, in the course of an irreversible process. For example, energy dissipation as heat due to entropy.

unified mass unit Chem.
See atomic mass unit.

unit matrix Math.
It is a diagonal matrix with all its diagonal elements equal to unity. Usually denotes as I. For example, a (3 x 3) unit matrix is

unit matrix

In general, if A is a square matrix of order (n x n) and I is also of the same order, then

IA = AI = A

universal indicator Chem.
A mixture of acid-base indicators, often in the form of solution, that changes color over a range of pH. For example, strong acids (pH < 2.0) give red color, weak acids give yellow or orange, weak alkalis give blue and strong alkalis give violet color. For neutral sample, the color is green, which is normally the default color of the indicator itself.

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