Rod(redirected from enamel rod)
Also found in: Dictionary, Thesaurus, Medical, Legal, Financial, Wikipedia.
English units of measurement
Customary Units of Weights and Measures
Units of Weight
Units of Length and Area
Units of Liquid Measure
Units of Dry Measure
Differences between American and British Systems
Many American units of weights and measures are based on units in use in Great Britain before 1824, when the British Imperial System was established. Since the Mendenhall Order of 1893, the U.S. yard and pound and all other units derived from them have been defined in terms of the metric units of length and mass, the meter and the kilogram; thus, there was no longer any direct relationship between American units and British units of the same name. In 1959 an international agreement was reached among English-speaking nations to use the same metric equivalents for the yard and pound for purposes of science and technology; these values are 1 yd=0.9144 meter (m) and 1 lb=0.45359237 kilogram (kg). In the United States, the older definition of the yard as 3,600/3,937 m has continued to be used in many instances for surveying, the corresponding foot (1,200/3,937 m) being known as the survey foot; the survey foot will become obsolete in 2023.
The English units of measurement have many drawbacks: the complexity of converting from one unit to another, the differences between American and British units, the use of the same name for different units (e.g., ounce for both weight and liquid capacity, quart and pint for both liquid and dry capacity), and the existence of three different systems of weights (avoirdupois, troy, and apothecaries'). Because of these disadvantages and because of the wide use of the much simpler metric system in most other parts of the world, there have been proposals to do away with the U.S. Customary System and replace it with the metric system.
See L. J. Chisholm, Units of Weights and Measure: International and U.S. Customary (U.S. National Bureau of Standards, 1967).
(also rod cell), a photoreceptor of the human and lower vertebrate eye. The rod cells respond to faint light. They and the cone cells are located in the outermost part of the retina. The cells consist of a basal synapse (connected with deeper-lying retinal cells), the nucleus, an internal segment containing ergastoplasm, the myoid (a contractile element of the rod cells), the ellipsoid (a mass of mitochondria), and an external segment made up of disks. A connective fiber with nine pairs of threads typical of cilia and departing from a pair of centrioles unites the internal and external segments. The disks of the outer segment, which are composed partly of visual pigment, are formed by an invagination of the cytoplasmic membrane. At the retinal periphery, there are more rod cells than cone cells. The retinas of nocturnal and crepuscular animals contain only rods.
REFERENCEVinnikov, la. A. Tsitologicheskie i molekuliarnye osnovy retseptsii. Leningrad, 1971.
O. G. STROEVA
in the theory of oscillations, an elastic solid body whose length greatly exceeds its transverse dimensions. When a rod is excited, for example, by an impact, free oscillations arise in the rod. The oscillatory displacements of the particles of the rod may be directed either along the rod’s axis—longitudinal oscillations—or perpendicular to the axis—torsional and flexural oscillations. For torsional oscillations, any cross section of the rod is twisted with respect to an adjacent cross section. For flexural oscillations, the points of the axis of the rod are displaced in a transverse direction, and fibers parallel to and lying on various sides of the axis undergo tensile and compressive strains.
Any oscillation of a rod may be represented as the sum of the simplest sinusoidals of the various types of natural oscillations in the rod. The frequencies f of the oscillations depend on the length l of the rod, the density p of the material, the shape and area S of the cross section, the elastic reaction to the given type of deformation, and the conditions of attachment of the rod’s ends. For example, for longitudinal oscillations of a free rod,
where E is Young’s modulus and n is an integer corresponding to the number of the harmonic component. For torsional oscillations of a round free rod,
where G is the shear modulus. In the case of flexural oscillations, the natural frequencies do not form a harmonic series, since the rate of propagation of flexural waves is dependent on frequency. For a rod secured at both ends,
where I is the moment of inertia of the cross section with respect to a neutral axis of the rod and the coefficient αn assumes the values α1 = 4.73, α2 = 7.85,. . . The form of the free oscillations of the rod depends on which of the free oscillations are found in the spectrum; this, in turn, is determined by the method of excitation.
Under the action of a sinusoidal driving force the rod oscillates at the frequency of the force f (forced oscillations). When the frequency of the force coincides with one of the rod’s natural frequencies, the phenomenon of resonance occurs.
The practical importance of oscillations of a rod is varied. Any beam in a structural design may be considered as a rod on whose natural frequencies the strength of the structure depends. Dangerous oscillations arising along a ship’s length because of an engine imbalance may be considered as oscillations of a rod. Rods are used in some musical instruments, such as xylophones. A tuning fork is a curved rod with two free ends.
REFERENCESMorse, P. Kolebaniia i zvuk. Moscow-Leningrad, 1949. (Translated from English.)
Strutt, J. W. (Lord Rayleigh). Teoriia zvuka, 2nd ed., vol. 1. Moscow, 1955. (Translated from English.)