A temperature scale with the ice point at 32° and the boiling point of water at 212°.
Conversion with the Celsius (centigrade temperature scale)
2. A propeller, especially when the emphasis is upon its function of moving air rather than propelling.
The unit of electrical capacitance, the capacitance of a condenser between the plates of which there is a difference of potential of 1 volt when it is charged by a quantity of electricity equal to 1 coulomb.
The product of the Avogadro constant and the elementary charge, e, F =
Self-explanatory compounds include: fatigue crack, fatigue failure, fatigue load, fatigue resistance, fatigue test.
2. State of the human organism after exposure to any type of physical or psychological stress (e.g., pilot fatigue).
2. The point at which a signal enters a circuit or device, as antenna feed.
3. The signal entering a circuit or device; input.
2. Information, as to progress, results, etc., returned to an originating source.
3. In aeronautics, the transmittal of forces initiated by aerodynamic action on control surfaces or rotor blades to the cockpit controls; the forces so transmitted.
A prefix meaning multiplied by 10-15.
2. A line or network of radar or radio stations for detection of a satellite in orbit.
3. A stationary plate or vane projecting from the upper surface of an airfoil, substantially parallel to the airflow, used to prevent spanwise flow.
A unit of length equal to 10-13 centimeters.
Transverse, oblique, and grid map projections are examples of fictitious projections.
The length of the fictitious year is the same as that of the tropical year, since both are based upon the position of the sun with respect to the vernal equinox.
The L-shaped corner marks and the + mark near the picture center, which are on the focal plane of the Tiros vidicon camera are fiducial marks. Their appearance on the image permits various calibrations such as determination of the degree of enlargement needed to fit the picture to the rectification grids, etc.
One may speak of a gravitation field, magnetic field, electric field, pressure field, temperature field, etc. If the quantity specified at each point is a vector quantity, the field is said to be a vector field.
Although field intensity is commonly used, it should be noted that this does not follow the strict radiometric definition of intensity, i.e., flux per unit solid angle.
2. = signal strength, in radar.
3. = electric-field strength.
2. The separation of a wanted component of a time series from any unwanted residue (noise).
2. A projecting flat plate or structure, as a cooling fin.
Usage is sometimes restricted to period of main chamber burning when small igniter chambers are used, especially with igniter idle provisions where the igniter may burn for some significant period prior to main chamber fire.
2. To launch a rocket.
2. The action or event of launching a rocket.
For reversible processes the mechanical work is equal to the expansion against the pressure forces, i.e.,
For open systems the variation of total rather than specific quantities is important:
If a system contains the possibility of nonmechanical work, such as work done against an electric field, this work must be included in the first law.
See second law of thermodynamics, third law of thermodynamics, energy equations.
Fission may occur spontaneously or may be induced by capture of bombarding particles. In addition to the fission fragments, neutrons and gamma rays are usually produced during fission.
The term properly is applicable to nuclei that undergo fission by neutrons of thermal energies; but it sometimes is applied loosely to cases where the neutron must be of high energy, an in U238 is fissionable by fast neutrons.
2. A notation in which the base point is assumed to remain fixed with respect to one end of the numeric expressions.
The flame deflector may be a relatively small device fixed to the top surface of the pad surrounded by the framework of the launcher, or it may be a heavily constructed piece of metal mounted as a side and bottom of a flame bucket. In the latter case, the deflector may be perforated with numerous holes connected with a source of water, bending at an angle of about 45° into the line of the exhaust stream. During thrust buildup and the beginning of the launch, a deluge of water pours from the holes in such a deflector to keep it from melting. See deluge collection pond.
2. In a captive test, an elbow in the exhaust conduit or flame bucket that deflects the flame into the open.
The Flamsteed number is used for stars numbered in Flamsteed's British Catalogue of 1725. For stars which do not appear in Flamsteed's catalog, numbers from other catalogs are used. See Bayer letter.
Flares may appear within minutes and fade within an hour. They cover a wide range of intensity and size, and they tend to occur between sunspots or over their penumbrae.
Flares are related to radio fadeouts and terrestrial magnetic disturbances.
Flares eject high energy protons which present a serious hazard to men in unshielded spacecraft.
2. Pyrotechnic devices used for signaling or to provide illumination.
3. An expansion at the end of a cylindrical body as at the base of a rocket.
Of the earth, the ratio of the difference between the equatorial radius (major semiaxis) and the polar radius (minor semiaxis) of the earth to the equatorial radius. Also called compression. See astronomical constants.
The flattening of the earth is the ellipticity of the spheroid and equals the ellipticity of the ellipse forming a meridional section the spheroid. If a and b represent the major and minor semiaxes of the spheroid, and f is the flattening of the earth,
2. An instance of such a movement.
2. A test of a component part of a flying vehicle, or of an object carried in such a vehicle, to determine its suitability or reliability in terms of its intended function by making it endure actual flight.
2. A similar bistable device with an input which allows it to act as a single-stage binary counter.
Floating point corresponds to multiplication using powers of 10; for example, 186,000 can be represented as 1.86 * 105. By shifting the point so that the number of significant digits in any quantity does not exceed machine capacity, widely varying quantities can be handled. The scale factor may be fixed for each problem, or indicated along with the digits and sign for each quantity.
The emission spectra usually studied are those of calcium and hydrogen; e.g., bright calcium flocculi, and dark or bright hydrogen flocculi. Measures of the extent of these three kinds of flocculi are tabulated in the quarterly Bulletin of Character Figures of Solar Phenomena, Zurich, Int. Astron. Union.
2. A buoyant landing gear, usually called floats.
A flow chart is a more detailed representation than a diagram.
This concept is only approximated by actual liquids and gases.
The size of the fluid parcel cannot be given precise numerical definition but it must be large enough to contain a great number of molecules and small enough so that the properties assigned to it are approximately uniform within it.
2. In nuclear physics generally, the number of radioactive particles per unit volume times their mean velocity.
In radar, flux density commonly is referred to as power density. It is essential to understand that the flux density of radiation is in no sense a vector quantity, because it is the sum of the flux corresponding to all ray directions incident upon one side of the unit area.
2. Alternate FM or AM operations.
2. A point having specific significance relative to a geometrical figure. See ellipse, hyperbola, parabola.
The foot (international) is exactly 0.3048 meter.
The American Survey foot is 0.3048006 meter.
The old U.S. foot, used prior to July 1, 1959, was 0.3048006 meter.
A unit of illuminance, incident light, or illumination equal to 1 lumen per square foot. This is the illuminance provided by a light source of one candle at a distance of 1 foot, hence the name. Compare lux, phot.
Full sunlight with zenith sun produces an illuminance of the order of 10,000 foot-candles on a horizontal surface at the earth's surface. Full moonlight provides an illuminance of only about 0.02 foot-candle also at earth's surface. Adequate illumination for steady reading is taken to be about 10 foot-candles; that for close machine work is about 30 to 40 foot-candles.
A unit of luminance (or brightness) equal to 1 /
candle per square foot, or 1 lumen per square foot. In Great Britain this is also called the equivalent foot-candle.
Forbidden lines of oxygen appear, for example, in the aurora.
The Forbush decrease is believed to be caused by a shielding effect of the magnetic fields contained in the plasma cloud emitted from the sun at the time of the flare.
The cause of the acceleration of material bodies measured by the rate of change of momentum produced on a free body.
See constellation.
In Rayleigh scattering, forward scatter accounts for half of the total. As the particle size increases above the Rayleigh limit, an increasing fraction of the total scattering is forward scattering.
and
When f(x) is an even function, only the cosine terms appear; when f(x) is odd, only the sine terms appear.
The conditions on f(x) guaranteeing convergence of the series are quite general, and the series may serve as a root-mean-square approximation even when it does not converge.
If the function is defined on an infinite interval and is not periodic, it is represented by the Fourier integral. By either representation, the function is decomposed into periodic components whose frequencies constitute the spectrum of the function. The Fourier series employs a discrete spectrum of wavelengths 2 L / n(n = 1,2,...); the Fourier integral requires a continuous spectrum.
See Fourier transform.
The Fourier transform has the same uses as the Fourier series: for example, the integrand F(u) exp (iux) is a solution of a given linear differential equation, so that the integral sum of these solutions is the most general solution of the equation.
When the variable u is complex, the Fourier transform is equivalent to the Laplace transform.
See Fourier integral, spectral function.
Foveal vision permits much higher resolution than does parafoveal vision and is the normal mode of seeing under daytime conditions.
Fraunhofer lines are designated by letters, as the K-line, or by wavelength, as the 4046-angstrom line of iron.
The major Fraunhofer lines are:
| anstroms | Line due to | |
| A | 7594 | Telluric oxygen |
| B | 6867 | Telluric oxygen |
| C | 6563 | hydrogen, H
|
| D1 | 5896 | sodium |
| D2 | 5890 | sodium |
| D3 | 5876 | helium |
| E | 5270 | iron and calcium |
| b1 | 5184 | magnesium |
| F | 4861 | hydrogen, H
|
| G | 4308 | iron (and calcium) |
| H | 3968 | calcium |
| K | 3934 | calcium |
If the antenna has a well-defined aperture a in a given aspect, the Fraunhofer region in that aspect is commonly taken to exist at distances greater than 2a2 /
from the aperture,
being the wavelength. 2. The free and unhampered motion of a body along a Keplerian trajectory, in which the force of gravity is counterbalanced by the force of inertia. See weightlessness.
In a free gyro, output signals are produced by gimbal angular displacements which correspond to components of the angular displacement of the base.
2. A gyro not provided with an erection system, i.e., a gyro free to move about its axes.
2. Flow about a body in which the number of collisions between the molecules of the fluid is negligible compared with the collisions between these molecules and the body. Also called free molecular flow. See rarefied gas dynamics, note.
Interest centers on three radicals, atomic hydrogen (H), atomic nitrogen (N), and the amine radical (NH). In their free state, they are highly active, combining with each other or with other substances to form other stable molecules, and yielding in the process energies well in excess of those available from conventional chemical fuels. Their use in propulsive systems, depends upon their being isolated and available in bulk, either in pure form or dissolved in a desired concentration in another fuel. See aeroduct.
Radio signal strength measurements are often expressed in terms of decibels above or below free-space values at a given distance from the transmitter. A free-space radiation pattern would show only the minor and major lobes of the antenna and not the interference pattern normally produced by reflection from the earth's surface.
2. Pertaining to the free stream, sense 1, as in free-stream dynamic pressure, free-stream flow, free-stream Mach number, free-stream static pressure, free-stream temperature, free-stream turbulence, free-stream velocity. See remote velocity.
Both pressure and speed are constant along a free streamline.
2. = free progressive wave.
Of a function periodic in time, the reciprocal of the primitive period. The unit is the cycle per unit time and must be specified.
In the International System the cycle per second is called the hertz (Hz).
Specific frequency bands used in radio and radar are often designated by names, numbers, or letters. The band designations as decided upon by the Atlantic City Radio Convention of 1947 and later modified by Comite Consultatif International Radio (CCIR) Recommendation No. 142 in 1953 were:
| Band number | Frequency range | Metric subdivision waves | Atlanctic City frequency subdivision | ||
|---|---|---|---|---|---|
| kc | |||||
| 4 | 3- | 30 | Myriametric | Very-low | VLF |
| 5 | 30- | 300 | Kilometric | Low | LF |
| 6 | 300- | 3,000 | Hectometric | Medium | MF |
| 7 | 3,000- | 30,000 | Decametric | High | HF |
| mc | |||||
| 8 | 30- | 300 | Metric | Very-high | VHF |
| 9 | 300- | 3,000 | Decimetric | Ultra-high | UHF |
| 10 | 3,000- | 30,000 | Centimetric | Super-high | SHF |
| 11 | 30,000- | 300,000 | Millimetric | Extremely high | EHF |
| 12 | 300,000- | 3,000,000 | Decimillimetric | -- | -- |
Description of bands by means of adjectives is arbitrary and the CCIR recommend that it be discontinued.
The designation ELF, extremely low frequency, has recently been proposed for the band extending from 3 kilocycles down to 1 cycle per second. These frequencies have been used for years in the study of lightning and associated phenomena and may be useful in communicating with spacecraft.
The frequency bands used by radar (radar frequency bands) were first designated by letters for military secrecy. Those designations were:
| P-band | 0.225 to 0.39 | 140 to 76.9 |
| L-band | 0.39 to 1.55 | 76.9 to 19.3 |
| S-band | 1.55 to 5.20 | 19.3 to 5.77 |
| X-band | 5.20 to 10.90 | 5.77 to 2.75 |
| K-band | 10.90 to 36.00 | 2.75 to 0.834 |
| Q-band | 36.00 to 46.00 | 0.834 to 0.652 |
| V-band | 46.00 to 56.00 | 0.652 to 0.536 |
2. A band of radio frequencies within which a station must maintain its modulated carrier frequency to prevent interference with stations on adjacent channels.
3. Any circuit over which telephone, telegraph, or other signals may be sent by an electric current.
The use of the term frequency deviation in this sense should be discouraged.
Mathematically, the frequency equation is the result of substituting a simple harmonic solution in the homogeneous differential equations of motion and the homogeneous boundary conditions. The frequency equation thus describes the free waves of the system. See group velocity.
Angle modulation of a sine-wave carrier in which the instantaneous frequency of the modulated wave differs from the carrier frequency by an amount proportional to the instantaneous value of the modulating wave. Compare pulse modulation, amplitude modulation, phase modulation, intensity modulation.
Combinations of phase and frequency modulation are commonly ref