1-49 NONDEGENERATIVE PARAMETRIC AMPLIFIER—A parametric amplifier that uses a pump signal frequency that is higher than twice the frequency of the input signal [11]. NONDIRECTIONAL—See OMNIDIRECTIONAL [10]. NONLINEAR DEVICE—A device in which the output does not rise and fall in direct proportion to the input [6] [7] [12]. NONLINEAR IMPEDANCE—An impedance in which the resulting current through the device is not proportional to the applied voltage [12]. NONLUMINOUS BODIES—Objects that either reflect or diffuse light that falls upon them [10]. NONRESONANT LINE—A transmission fine that has no standing waves of current or voltage [10]. NONTRIP-FREE CIRCUIT BREAKER—A circuit breaker that can be held in the ON position during an overcurrent condition [3]. NOR—A logic function of A and B that is true if both A and B are false [13]. NOR GATE—An OR gate that is followed by an inverter to form a binary circuit in which the output is a logic 0 if ANY of the inputs is a logic 1 and the output is a logic 1 only if ALL the inputs are a logic 0 [13]. NORMAL—The imaginary line perpendicular to the point at which the incident wave strikes the reflecting surface. Also called the perpendicular [10]. NOT CIRCUIT—A binary circuit with a single output that is always the opposite of the input. Also called an INVERTER CIRCUIT [13]. NPN—An NPN transistor is formed by introducing a thin region of P-type material between two regions of N-type material [7]. NULL—On a polar-coordinate graph, the area that represents minimum or 0 radiation [10]. NUMBER—(1) A mathematical entity that may indicate quantity or amount of units. (2) Loosely, a numeral. An abstract mathematical symbol for expressing a quantity. In this sense, the manner of representing the number is immaterial. Take 26, for example; this is its decimal form - but it could be expressed as a binary (base 2), octal (base 8), or hexadecimal (base 16) number [13]. NUMBER REPRESENTATION—The representation of numbers by agreed sets of symbols according to agreed rules [13]. NUMBER SYSTEM—Loosely, a number representation system. Any system for the representation of numbers (see POSITIONAL NOTATION) [13]. NUMERAL—(1) A discrete representation of a number. For example, twelve, 12, XII, 1100_{2}are four different numerals that represent the same number. (2) A numeric word that represents a number [13]. NUTATING—Moving an antenna feed point in a conical pattern so that the polarization of the beam does not change [18]. OCTAL NUMBER SYSTEM—A number system based on powers of eight. This system is used extensively in computer work [13].