“period”的概念、定义、翻译、参考文献-科学参考

period

Physics

See periodic motion.

Mathematics

If, for some value p, f(x + p) = f(x) for all x, the real function f is periodic and has period p. For example, cos x is periodic with period 2π‎ radians, since cos(x + 2π‎) = cos x for all x; or, using degrees, cos x° is periodic with period 360. Some authors restrict the use of the term ‘period’ to the smallest positive value of p with this property.

In mechanics, any phenomenon that repeats regularly may be called periodic, and the time taken before the phenomenon repeats itself is then called the period. Suppose that x = Asin(ω‎t + α‎), where A > 0, ω‎ and α‎ are constants. This may, for example, give the displacement x of a particle, moving in a line, at time t. The particle is thus oscillating about the origin. The period is the time taken for one complete oscillation and is equal to 2π‎/ω‎.

Chemistry

1. The time taken for one complete cycle of an oscillating system or wave.
2. See periodic table.

Computer

The time required for a periodic waveform—i.e. a waveform recurring at fixed intervals—to repeat itself.

Biology

See menstrual cycle.

Geology and Earth Sciences

1. Second-order geologic time unit which is the equivalent of the chronostratigraphic unit ‘system’. Periods are subdivided into epochs; together, several periods constitute an era. When used formally the initial letter of the term is often capitalized, e.g. the Devonian Period.
2. (T) The time that elapses between repetitions of the same phase of a wave-form, i.e. the time taken to complete one cycle. For a simple harmonic function, T = 2π‎/ω‎ where ω‎ is the angular velocity; for a wavetrain of single frequency f, T = 1/f = λ‎/V where λ‎ is the wavelength and V the phase velocity.

单词	period
释义	period Physics See periodic motion. Mathematics If, for some value p, f(x + p) = f(x) for all x, the real function f is periodic and has period p. For example, cos x is periodic with period 2π‎ radians, since cos(x + 2π‎) = cos x for all x; or, using degrees, cos x° is periodic with period 360. Some authors restrict the use of the term ‘period’ to the smallest positive value of p with this property. In mechanics, any phenomenon that repeats regularly may be called periodic, and the time taken before the phenomenon repeats itself is then called the period. Suppose that x = Asin(ω‎t + α‎), where A > 0, ω‎ and α‎ are constants. This may, for example, give the displacement x of a particle, moving in a line, at time t. The particle is thus oscillating about the origin. The period is the time taken for one complete oscillation and is equal to 2π‎/ω‎. Chemistry 1. The time taken for one complete cycle of an oscillating system or wave. 2. See periodic table. Computer The time required for a periodic waveform—i.e. a waveform recurring at fixed intervals—to repeat itself. Biology See menstrual cycle. Geology and Earth Sciences 1. Second-order geologic time unit which is the equivalent of the chronostratigraphic unit ‘system’. Periods are subdivided into epochs; together, several periods constitute an era. When used formally the initial letter of the term is often capitalized, e.g. the Devonian Period. 2. (T) The time that elapses between repetitions of the same phase of a wave-form, i.e. the time taken to complete one cycle. For a simple harmonic function, T = 2π‎/ω‎ where ω‎ is the angular velocity; for a wavetrain of single frequency f, T = 1/f = λ‎/V where λ‎ is the wavelength and V the phase velocity.
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