This paper analyzes the confinement mechanism of particles in a three-component dusty plasma with plasma fluctuations. The mechanism is based on the gain in electrical correlation energy of the plasma in the case of a reduction of its volume. We also show that minima of free energy of dust particles and ions exist when the distance between dust particles is equal to two Debye electronic radii and when the distance between ions is directed by the condition of plasma electrical neutrality. The total free energy of the plasma can also have a minimum provided that the normal charge transferred by electrons does not exceed ∼ 20% of the charge transferred by all negatively charged particles.

A new theory is proposed to extend the limit of the application of bulk ultrasonic pulses, which have been thought to be unsuitable for the evaluation of sound velocity in thin coating layers because of interference with echoes. This extension is accomplished by introducing the new concept of the group delay spectrum. We first made a model representing waves reflected from a coating layer and found that many acoustic properties, for example, sound velocity, acoustic impedance, and coating density, can be derived easily by a group delay analysis. Next, the theory was applied to the analysis of a layer plasmasprayed coated with alumina particles on a stainless steel substrate. To confirm the validity of the theory, we prepared coated specimens of varying thicknesses which covered from 0.16 mm to 0.48 mm, and we succeeded in evaluating sound velocity and coating density.

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A new analytical technique of the propagation of ultrasonic pulses in dispersive or nondispersive media is proposed. First, on the basis of the concept of group delay, we develop the theory as follows: (1) group delay is deduced directly from the Fourier transform of waveforms, and (2) cross-correlation theory is extended to a total measurement system which may include, for example, a sensor, couplant, amplifier, and A/D converter. Then, a fundamental result that the group delay between wave motions generated in a medium is exactly the same as that of corresponding waveforms observed by an observer is obtained. Next, this result is applied to improve the conventional pulse-echo method, and it is shown that by preparing two specimens of the same material but with different thicknesses, correct group delay in propagation can be obtained even though no physical or mechanical constants of the couplant or sensor may be known. In order to apply the results to the pulse-echo method, measurements of phase and group velocity in synthetic fused silica were also attempted.

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