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Q

  
q
   (NASA SP-7, 1965)
= dynamic pressure,
as the vehicle encountered maximum q 40 seconds after lift-off.
Q factors
   (Plasma Physics and Fusion Energy Glossary)
Ratio of power produced by fusion to power put into the reactor to heat the plasma and drive the magnetic fields. Q = 1 is the definition of scientific breakeven, where power out = power in. Economical fusion will require Q significantly greater than 1.
Q switch
   (Plasma Physics and Fusion Energy Glossary)
Optical switch used to rapidly change the Q of an optical resonator; utilized in the optical resonator of a laser to prevent lasing action until a high level of gain and energy storage are achieved in the laser medium. When the switch is triggered and rapidly increases the Q of the cavity, a stronger laser pulse is generated.
Q switched lasers
   (NASA Thesaurus)
A device for producing very short (about 30 ns)intense laser pulses by enhancing the storage and dumping of electronic energy in and out of the lasing medium.
Q-band
   (NASA SP-7, 1965)
A frequency band used in radar extending approximately from 36 to 46 kilomegacycles. See frequency band.
quadrant
   (NASA SP-7, 1965)
See sextant.
quadrature
   (NASA Thesaurus / NASA SP-7, 1965)
1. An elongation of 90 degrees, usually specified as east or west in accordance with the direction of the body from the sun. The moon is at quadrature at first and last quarters. Compare conjunction.
2. The situation of two periodic quantities differing by a quarter of a cycle.
quadrature amplitude modulation
   (NASA Thesaurus)
Amplitude modulation in which the signal is 90 degrees out of phase with the carrier which it modulates.
quadrupoles
   (NASA Thesaurus)
A linear accelerator having four longitudinal vanes in its resonating cavity, which are shaped to create RF electric fields that simultaneously accelerate, bunch, and focus the charged particle beam.
qualitative analysis
   (NASA Thesaurus)
An analysis in which some or all of the components of a sample are identified.
quality control
   (NASA Thesaurus)
An aggregate of functions designed to insure adequate quality in manufactured products by initial critical study of engineering design, materials, processes, equipment, and workmanship followed by periodic inspection and analysis. Used for reliability control.
quality factor
   (NASA SP-7, 1965)
(symbol Q)
A measure of the sharpness of resonance or frequency selectivity of a resonant vibratory system having a single degree of freedom, either mechanical or electrical. See vibration. In a mechanical system, this quantity is very nearly equal to one-half the reciprocal of the damping ratio. When used with reference to a lightly damped system, it is also approximately equal to the following: (1) transmissibility at resonance; (2) pi over lower case delta where delta lower case is the logarithmic decrement; (3) two pi W over delta W where W is the stored energy and triangle W the energy dissipation per cycle; and (4) f sub lambda over triangle f where fr is the resonance frequency and triangle W is the bandwidth between the half-power points. Historically the letter Q was an arbitrarily chosen symbol to designate the ratio of reactance to resistance of a circuit element. The name quality factor was introduced later.
quanta
   (NASA SP-7, 1965)
See quantum theory.
quantiles
   (NASA Thesaurus)
The values that mark frequency distribution interval boundaries that are determined by arranging a set of N observations in order of magnitude and marking off equal parts (N/P) of the total population P.
quantity
   (NASA SP-7, 1965)
See number.
quantization
   (NASA SP-7, 1965)
The process of converting from continuous values of information to a finite number of discrete values.
quantize
   (Global Land Information System Glossary - USGS)
To limit the possible values of (e.g., quantity) to a discrete set of values by quantum mechanical rules (Webster's II, 1994).
quantum chromodynamics
   (NASA Thesaurus)
A gauge theory describing the interaction between quarks and gluons. Used for color (particle physics) and QCD.
quantum dots
   (NASA Thesaurus)
Small (30 nm to 1 micron) metal or semiconductor structures that hold a discrete number of electrons; the number of electrons can be altered by modifying the electrostatic environment of the dot.
quantum efficiency
   (NASA Thesaurus)
A measure of the efficiency of conversion or utilization of light or some other form of energy.
quantum electronics
   (NASA Thesaurus)
The branch of electronics that essentially deals with lasers and laser devices which require quantum theory for their exact description.
quantum numbers
   (NASA Thesaurus)
A number assigned to one f the various values of a quantized quantity in its descrete range. The quantum numbers arise from the mathematics of the wave equations. When the quantity has a quantum, the quantum number is the number of such quantums. A state may be described by giving a sufficient set of compatible numbers. In the cutomary forumlations, each quantum number is either an interger (which may be positive, negative, or zero) or an odd half-integer.
quantum theory
   (NASA Thesaurus / NASA SP-7, 1965)
The theory first stated by Max Planck (before the Physical Society of Berlin on December 14, 1900) that all electromagnetic radiation is emitted and absorbed in quanta , each of magnitude h nu , h being the Planck constant and nu the frequency of the radiation. See radiation laws.
quantum wells
   (NASA Thesaurus)
Effective potential wells created by a minimum in the conduction band or a maximum in the valence band that arises when a smaller band-gap semiconductor is sandwiched between a larger band-gap semiconductor.
quark parton model
   (NASA Thesaurus)
A theoretical model which summarizes our understanding of how protons and neutrons are made up of the fundamental subparticles called quarks.
quartz
   (NASA Thesaurus)
Crystalline silica, an important rock-forming mineral.
quasars
   (High Energy Astrophysics Dictionary- GSFC)
A specific type of quasi-stellar source. A stellar-appearing object of very large redshift that is a strong source of radio waves; presumed to be extragalactic and highly luminous.
quasi-geostrophic equilibrium
   (NASA SP-7, 1965)
See equivalent barotropic model.
quasi-Lagrangian coordinates
   (NASA SP-7, 1965)
A system of mixed Eulerian and Lagrangian coordinates. At least one coordinate of each fluid parcel must therefore by unvarying with time.
quefrencies
   (NASA Thesaurus)
In cepstral analysis, the frequency of periodic ripples in a spectra of a signal that contains echoes. Quefrencies are expressed in cycles per hertz or in seconds.
quenching (atomic physics)
   (NASA Thesaurus)
Phenomena in which very strong electric fields cause the orbit of an electron or atom to precess rapidly so the average magnetic moment associated with its orbit angular momentum is reduced to zero.
quenching (cooling)
   (NASA Thesaurus)
Rapid cooling as in metallurgy. Used for flame quenching.
query languages
   (NASA Thesaurus)
Command languages used to search and retrieve information.
quiet sun
   (NASA SP-7, 1965)
The sun when it is free from unusual radio wave or thermal radiation such as that associated with sunspots. See IQSY.
quinoxalines
   (NASA Thesaurus)
A group of heterocyclic compounds consisting of a benzene ring condensed with a diazine ring.
quintant
   (NASA SP-7, 1965)
See sextant.
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