Determination of phase velocities of a circular helix using the method of internal constraints

1970 ◽  
Vol 67 (2) ◽  
pp. 509-521 ◽  
Author(s):  
J. W. Lincoln ◽  
M. Nikkhah ◽  
E. Volterra
Keyword(s):  
Elementary Theory ◽  
Internal Constraints ◽  
Phase Velocities ◽  
Circular Helix

AbstractA procedure is described to determine phase velocities of a circular helix. Computations are made for three helix configurations using the method of internal constraints. The results so obtained are compared with the results obtained by using the elementary theory proposed by J. H. Michell, and the extended elementary theory proposed by A. B. Basset.

Acoustic Phase Velocity Measurements along General Directions in Non-Isotropic Crystals. I. Elastic Properties of Monoclinic K3Co(CN)6

1971 ◽  
Vol 49 (12) ◽  
pp. 1597-1605 ◽  
Author(s):  
T. H. Chou ◽  
S. L. McBride ◽  
N. Rumin
Keyword(s):  
Elastic Constants ◽  
Experimental Error ◽  
Acoustic Velocity ◽  
Acoustic Energy ◽  
Perturbation Calculation ◽  
Velocity Measurements ◽  
Phase Velocities ◽  
Low Symmetry ◽  
Acoustic Phase

The complete elastic constants tensor of monoclinic potassium cobalticyanide [K3Co(CN)6] has been determined from measured ultrasonic phase velocities. These were obtained as a function of direction in several crystal planes by measuring the acoustic energy reflection coefficient at a liquid–solid interface as a function of angle and plane of incidence. The measurements were made at 27.6 MHz in p-xylene at 21.5 °C. The elastic constants were determined using an existing perturbation method. Velocities calculated from the derived elastic constants are in agreement with the measured velocities to within experimental error and the approximations in the perturbation calculation. The usefulness of this method for the determination of the elastic constants of low symmetry crystals is thus established. The Debye temperature of K3Co(CN)6 is estimated from the results to be 290 ± 10 °K with a corresponding mean acoustic velocity of 2560 ± 80 m/s.

Whistler emission through transition radiation by a modulated electron beam spiralling in a magnetoplasma

2000 ◽  
Vol 63 (3) ◽  
pp. 285-295 ◽  
Author(s):  
M. STARODUBTSEV ◽  
C. KRAFFT
Keyword(s):  
Magnetic Field ◽  
Electron Beam ◽  
External Magnetic Field ◽  
Transition Radiation ◽  
Physical Processes ◽  
Phase Velocities ◽  
Electric Dipoles ◽  
Wave Emission ◽  
Loop Antennas

Transition radiation from the zone of injection of a modulated electron beam spiralling into a magnetoplasma has been identified as whistler waves propagating quasiparallel to the external magnetic field. The characteristics of the radiation are similar to the emission by localized sources, such as loop antennas and electric dipoles: resonance-cone structures at low plasma densities and energy flow along the external magnetic field at higher densities, with a diverging radiation pattern and with whistler phase velocities inversely proportional to the plasma frequency. These studies should contribute to a wider understanding of the physical processes connected with the injection of charges in a magnetoplasma – either from a gun on board a spacecraft or in a plasma chamber – and thus allow the determination of appropriate radiator characteristics in order to control, to some extent, plasma perturbations and wave emission in the region of the injector.

New techniques for the determination of surface wave phase velocities

1968 ◽  
Vol 58 (3) ◽  
pp. 1021-1034 ◽  
Author(s):  
S. Bloch ◽  
A. L. Hales
Keyword(s):  
Phase Velocity ◽  
Rayleigh Waves ◽  
World Wide ◽  
Velocity Dispersion ◽  
Cross Product ◽  
New Techniques ◽  
Phase Velocities ◽  
Phase Velocity Dispersion ◽  
The World

abstract A number of new techniques have been developed for the determination of phase velocities from the digitized seismograms from pairs of stations. One of these techniques is to Fourier analyze the sum (or difference) of the two seismograms after time shifting in steps to correspond to steps in phase velocity. The amplitude of the summed seismogram is a maximum for any particular period when both seismograms are in phase at that period. Another method is to pass both seismograms through a narrow bandpass digital filter centered at various periods and form the cross product of the filtered seismograms, after time shifting. The average of the resultant time series is a maximum when the two signals are in phase. The computer output is a matrix consisting of amplitudes or averages as a function of phase velocity and period. The phase velocity dispersion is determined from the contoured matrix. Using these techniques, interstation phase velocities of Rayleigh waves have been determined for the “World Wide Network Standard Stations” at Pretoria, Bulawayo and Windhoek. The method using cross-products is the most efficient.

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