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The Doppler effect (also Doppler shift) is the change in the frequency of a wave in relation to an observer who is moving relative to the source of the wave. [ 1 ] [ 2 ] [ 3 ] The Doppler effect is named after the physicist Christian Doppler , who described the phenomenon in 1842.
A niobium-based 1.3 GHz nine-cell superconducting radio frequency to be used at the main linac of the International Linear Collider [8] A cross section view of the niobium superconducting radio frequency cavity at Fermilab. A large variety of RF cavities are used in particle accelerators.
In the physical sciences and in telecommunication, the term frequency shift may refer to: Any change in frequency; A Doppler shift; In facsimile, a frequency modulation system where one frequency represents picture black and another frequency represents picture white; Spectrum shifting in signal processing, see Discrete Fourier transform#Shift ...
Radio frequency (RF) is the oscillation rate of an alternating electric current or voltage or of a magnetic, electric or electromagnetic field or mechanical system in ...
The perturbation of this alignment of the nuclear spins by a weak oscillating magnetic field, usually referred to as a radio-frequency (RF) pulse. Detection and analysis of the electromagnetic waves emitted by the nuclei of the sample as a result of this perturbation. Similarly, biochemists use NMR to identify proteins and other complex ...
Chemical shift δ is usually expressed in parts per million (ppm) by frequency, because it is calculated from [5] =, where ν sample is the absolute resonance frequency of the sample, and ν ref is the absolute resonance frequency of a standard reference compound, measured in the same applied magnetic field B 0.
The hydrogen line frequency lies in the L band, which is located in the lower end of the microwave region of the electromagnetic spectrum. It is frequently observed in radio astronomy because those radio waves can penetrate the large clouds of interstellar cosmic dust that are opaque to visible light.
Regardless, radars that employ the technique are universally coherent, with a very stable radio frequency, and the pulse packets may also be used to make measurements of the Doppler shift (a velocity-dependent modification of the apparent radio frequency), especially when the PRFs are in the hundreds-of-kilohertz range. Radars exploiting ...