NET BUOYANCY . The weight of fluid displaced by a 

 floating or submerged body, minus the weight of the 

 body. Thus, an object floating has positive buoy- 

 ancy; an object sunk has negative buoyancy; and an 

 object in the hovering state has zero (or neutral) 

 buoyancy. (27) 



NET PLANKTON . Those plankton which can be removed 

 from the water by filtration through a fine net. 

 (See MARINE LIFE) 



NEURISTOR . A microelectronic device used in a syn- 

 thetic structure device used to duplicate the com- 

 mand transmission phenomena of the nerve cells of 

 living animals. 



Neuristors are active one-dimensional fiber- 

 like devices with properties such that a network of 

 them used in information processing can perform ar- 

 bitrarily complex logical functions without any 

 additional connections or elements. 



NEVE . More or less loose, granular ice in transi- 

 tion from snow to GLACIER ICE. Neve, in being 

 buried about 100 feet, becomes compacted and gradu- 

 ally changes to glacier ice. The upper layers of 

 glaciers and SHELF ICE are usually composed on 

 n^v^. (25) 



NICHE . See BIOTOPE . 



NIMBOSTRATUS . A dark, low, shapeless cloud layer 

 (mean upper level below 6,500 feet) usually nearly 

 uniform; the typical rain cloud. When precipitation 

 falls from nimbostratus , it is in the form of con- 

 tinuous or intermittent rain or snow, as contrasted 

 with the showery precipitation of cumulonimbus. 

 (17) 



NIMBUS . A characteristic rain cloud. The term is 

 not used in the international cloud classification 

 except as a combining term, as cumulonimbus. (17) 



NIC . National Institute of Oceanography (England). 



NIP . The cut made by waves in a shore line of 

 emergence. (11) 



NIRS. National Institute of Radiological Sciences. 



as uncombined metal in nature. It always exhibits 

 a relatively large electro-positive potential which 

 is not dependent upon the existence of chemical 

 films on its surface. Platinum, gold and silver are 

 noble metals. (35) 



NOCTILUCENT CLOUD . A luminous cirrus -like cloud 

 occasionally seen a great distance (about 50 miles) 

 above the surface of the earth. It is faintly 

 visible when the sun is a short distance below the 

 horizon, when it is illuminated by the sun. Its 

 nature and origin are obscure. (17) 



NODAL LINE . A line in an oscillating area along 

 which there is little or no rise and fall of the 

 tide. (14) 



NODAL POINT . The no-tide point in an AMPHIDROMIC 

 REGION. (14) 



NODAL ZONE . An area at which the predominant 

 direction of the LITTORAL TRANSPORT changes. (11) 



NODC . National Oceanographic Data Center, Washing- 

 ton, D. C. 



NODE CYCLE . Period of approximately 18.61 Julian 

 years required for the regression of the moon's 

 nodes to complete a circuit of 360° of longitude. 

 It is accompanied by a corresponding cycle of 

 changing inclination of the moon's orbit relative 

 to the plane of the earth's equator with resulting 

 inequalities in the rise and fall of the tide and 

 velocity of the tidal current. (14) 



NODES. In standing-wave patterns, points at which 

 the acoustic pressure, or other measure of acoustic 

 energy, exhibit minimum values, or are zero, are 

 known as nodes. (4) 



NOISE . Noise is any undesired sound. By exten- 

 sion, noise is any unwanted disturbance within a 

 useful frequency band, such as undesired electric 

 waves in a transmission channel or device. (1) 



NOISE LEVEL . The transmission level of interference 

 computed from its equivalent plane wave intensity 

 is usually spoken of as the noise level. (4) 



NITROGENATION . See SATURATION. 



NITROGEN NARCOSIS . Like most inert gases, nitro- 

 gen in air or N2 - 02 mixtures breathed at high 

 ambient pressure can decrease mental clarity, 

 impair judgment and produce poor muscle coordina- 

 tion in a manner similar to that found in alcohol 

 intoxication. The narcotic effect is related to 

 the PARTIAL PRESSURE of inspired nitrogen; it is 

 therefore a function of depth of diving and the 

 percentage of nitrogen in the respired gas. 

 Nitrogen narcosis is not in itself harmful, but 

 when air (807o nitrogen) is breathed (as in OPEN 

 CIRCUIT SCUBA equipment) at depths below about 

 60 - 80 feet the resulting impaired judgment and 

 incoordination begins to interfere with the diver's 

 performance and predispose him to accidents. The 

 narcotic effects increase progressively with 

 depth until at about 280 - 300 feet even routine 

 tasks become extremely difficult. As in the 

 drinking of alcohol, personality, motivation, 

 and training in a specific task account for the 

 different reactions among different men. 



In orthodox deep sea diving narcosis can be 

 reduced by substitution of helium for nitrogen. 

 Unfortunately, on deep dives of short duration 

 typical of underwater swimming, the use of helium 

 in place of nitrogen increases the decompression 

 time required to avoid BENDS, (37) 



NMDL . Navy Mine Defense Laboratory, Panama City, 

 Florida. 



NOBLE METAL . An inert metal which is usually found 



NOISE RADIALS . The brightening of all range points 

 on a specific PPI bearing, caused by the reception 

 of noise from the direction indicated. (7) 



NOL. Naval Ordnance Laboratory, U. S. Navy, White 

 Oak, Maryland. 



NOL CORONA . Naval Ordnance Laboratory, Corona, 

 California. 



NOMAD (NAVY OCEANOGRAPHIC AND METEOROLOGICAL AUTO- 

 MATIC DEVICE) . NOMAD measures and transmits 

 weather data. This unit has been given periodic 

 sea trials since 1957 while anchored in 2,000 

 ■fathoms in the Gulf of Mexico. It has successfully 

 operated under extreme weather conditions and has 

 remained on station for periods up to 6 months. 

 The buoy is 20-feet long, 10-feet wide, and 8-feet 

 deep. It weighs 12 tons when loaded and has 18 

 tons of buoyancy. The unit is moored with a poly- 

 propylene and dacron line. Wind velocity, air tem- 

 perature, surface water temperature, and barometric 

 pressure are telemetered at 5540 kc in Morse code. 

 Each dot and dash consists of a series of high 

 energy spikes rather than a continuous tone. This 

 method of transmission, called pulse-recurrent FM, 

 allows greater range (800 miles) with less overall 

 power expenditure (200 watts average) . The unit 

 is powered with 12-volt, wet cell batteries and 5- 

 watt wind chargers. (35) 



NOMINAL BANDWIDTH . The nominal bandwidth of a fil- 

 ter is the difference between the nominal upper and 

 lower cutoff frequencies. This difference may be 



82 



