Biomedical subjects

P L Marston

Publications and source records attributed to P L Marston.

4 recordsLinked to original sources

PubMed2001

Passive stabilization of capillary bridges in air with acoustic radiation pressure.

Long liquid capillary bridges are normally unstable because of the growth of a mode where one end becomes slender while the other becomes rotund. This Rayleigh-Plateau instability was suppressed for weightless bridges on NASA's KC-135 aircraft by placing the bridge in an acoustic standing wave. With an appropriate acoustic wavelength and amplitude the radiation pressure automatically squeezes more on the rotund portion of the bridge so as to suppress the growth of the relevant capillary mode. Stabilization is a natural consequence of the interaction with the steady sound field.

Journal Article↗

PubMed2001

Generalized optical theorem for scatterers having inversion symmetry: applications to acoustic backscattering.

The far-field acoustic scattering amplitudes for the scattering of plane waves by targets having inversion symmetry obey a generalized optical theorem in the absence of dissipation. The theorem allows a component of the complex scattering amplitude in an arbitrary direction to be expressed in terms of an angular integration involving scattering amplitudes evaluated at different angles. The result reduces to the usual optical theorem in the case of forward scattering. The theorem is applied to the backscattering by a perfectly soft sphere as a numerical example. The relevant integrand is shown to be oscillatory. Some potential applications to inverse problems, multiple scattering, and the verification of numerical algorithms are noted.

Journal Article↗

PubMed2001

Leaky helical flexural wave scattering contributions from tilted cylindrical shells: ray theory and wave-vector anisotropy.

At sufficiently high frequencies, cylindrical shells support a wave whose properties are analogous to those of the lowest antisymmetric Lamb wave on plates. When the shell is in water and the frequency exceeds the coincidence frequency, the flexural wave is a leaky wave that can be a major contributor to the scattering by tilted shells [G. Kaduchak, C. M. Wassmuth, and C. M. Loeffler, J. Acoust. Soc. Am. 100, 64-71 (1996)]. While the meridional ray-scattering contributions for such leaky flexural waves were previously modeled, the helical contribution can also be significant. A ray theory for those contributions is compared with the exact partial wave series (PWS) solution for infinitely long empty shells. The agreement between the ray theory and the PWS is only possible when a weak anisotropy of the flexural wave parameters is included in the evaluation of the ray theory. The anisotropy is determined numerically from the roots of a denominator in the PWS because approximations for the anisotropy from thin-shell mechanics are not applicable significantly above the coincidence frequency.

Journal Article↗

PubMed1998

Acoustic field interaction with a boiling system under terrestrial gravity and microgravity.

Pool boiling experiments from a platinum wire heater in FC-72 liquid were conducted under terrestrial and microgravity conditions, both with and without the presence of a high-intensity acoustic standing wave within the fluid. The purpose of this research was to study the interaction between an acoustic field and a pool boiling system in normal gravity and microgravity. The absence of buoyancy in microgravity complicates the process of boiling. The acoustic force on a vapor bubble generated from a heated wire in a standing wave was shown to be able to play the role of buoyancy in microgravity. The microgravity environment was achieved with 0.6 and 2.1-s drop towers. The sound was transmitted through the fluid medium by means of a half wavelength sonic transducer driven at 10.18 kHz. At high enough acoustic pressure amplitudes cavitation and streaming began playing an important role in vapor bubble dynamics and heat transfer. Several different fixed heat fluxes were chosen for the microgravity experiment and the effects of acoustics on the surface temperature of the heater were recorded and the vapor bubble movement was filmed. Video images of the pool boiling processes and heat transfer data are presented.

Acoustics↗