Thursday, September 19, 1991 1:00 p.m. Carl Bruch Department of Physics The University of Texas Although acoustical media are often stratified, either continuously (e.g., via sound speed gradients) or with discrete but penetrable layers, finite amplitude effects in stratified media have been all but ignored. By channeling the sound, however, stratification can maintain high acoustic…
Wednesday, April 24, 1991 4:00 p.m. Dr. James A. Kearns Applied Research Laboratories The University of Texas at Austin As part of a program to understand key aspects of long range propagation of sound over irregular topography, an investigation was made of the diffraction effects which occur near the top of hills and ridges. This…
Friday, April 19, 1991 4:00 p.m. Dr. Dennis McFadden Department of Psychology The University of Texas at Austin There is a phenomenon in auditory masking that has traditionally been viewed as a manifestation of an adaption-like effect in the auditory system. If a brief tonal signal is presented within a couple of milliseconds of the…
Friday, April 12, 1991 4:00 p.m. Dr. Ethan T. Vishniac Department of Astronomy The University of Texas at Austin The impulsive release of energy into a fluid gives rise to a spreading discontinuity (shock) whose behavior is usually observed to be quite regular. However, it can be shown that if the post-shock density is sufficiently…
Friday, April 5, 1991 4:00 p.m. John T. Post Department of Electrical and Computer Engineering, The University of Texas at Austin and Richard J. Silcox Structural Acoustics Branch, Mail Stop 463, Acoustics Division, NASA/Langley Research Center, Hampton, VA 23665 With the trend towards lighter weight for aerospace structures, the need to control the vibrations of…
Friday, March 29, 1991 4:00 p.m. Dr. Thomas Griffy Department of Physics The University of Texas at Austin At a previous acoustics seminar (October 29, 1990) the application of dispersion relations to acoustic propagation was discussed. Some of the results presented at that time and some of the papers on which the presentation was based,…
Friday, March 22, 1991 4:00 p.m. David Nelson Acoustic Systems Acoustical Research Facility Austin, Texas The “edge effect” is a natural consequence of sound absorption measurements in reverberation chambers, which comes about because the reverberant sound field is diffused everywhere except directly over the specimen. The effect causes inflated sound absorption coefficient readings which are…
Friday, March 8, 1991 4:00 p.m. Dr. C. L. Morfey Institute of Sound and Vibration Research, Southampton, United Kingdom Acoustical aspects of extracorporeal shock-wave lithotripsy (ESWL) will be outlined, with emphasis on simple time-domain models. ESWL is a clinical procedure now in routine use: it involves short-duration acoustic pulses (time scale of order 1 to…
Friday, February 22, 1991 4:00 p.m. Dr. Tom Muir Applied Research Laboratory The University of Texas at Austin Assigned to SACLANTCEN, 1986-89 In order to support ocean acoustic modeling and sonar performance prediction, it is necessary to acquire geoacoustic data on the sediment structures. The direct measurement of shear wave velocity and attenuation within the…
Friday, February 15, 1991 4:00 p.m. Bart Lipkens Graduate Student Mechanical Engineering Department The University of Texas at Austin The application of high intensity acoustics to several energy-related processes has recently experienced much renewed interest. Acoustic levels of 150 to 160 dB appear to be required at frequencies in the 1000-3000 Hz range. In a…
Friday, February 8, 1991 4:00 p.m. Peter D. Thorne Birkenhead, Merseyside, U .K. The measurement of sediment transport is a critical parameter in marine studies. It has traditionally been difficult to accurately quantify, and recently acoustics has been applied to solve this problem. To monitor the bedload transport of marine gravels, caused by turbulent tidal…
Wednesday, January 30, 1991 4:00 p.m. Frank A. Boyle and Nicholas P. Chotiros Applied Research Laboratories The University of Texas at Austin Following recent experimental results at sea that suggest the existence of a previously undetected type of acoustic wave in sandy sediments, an experiment was designed to detect and measure the speed of acoustic…
Monday, December 3, 1990 4:00 p.m. Robert L. Rogers Applied Research Laboratories The University of Texas at Austin A sea trip in the Gulf of Mexico was performed on the RV Longhorn. Tests were conducted on the plasma sound source (PSS) at various depths and energies. Basic information was obtained regarding the PSS acoustic signature…
Monday, November 19, 1990 4:00 p.m. Ping Wah Li Applied Research Laboratories and the Physics Department The University of Texas at Austin Experiments show that when a tissue is exposed to high intensity ultrasound, the temperature increase can be much more than that expected on the basis of linear theory. It is believed that this…
Thursday, November 15, 1990 4:00 p.m. Yang-Sub Lee Department of Mechanical Engineering The University of Texas at Austin A time domain computer algorithm for solving the KZK (Kokhlov-Zabolotskaya-Kuznetsov) nonlinear parabolic wave equation has been developed for pulsed, axisymmetric, finite amplitude sound beams. The KZK equation accounts consistently for the combined effects of the thermoviscous dissipation,…
Monday, November 5, 1990 4:00 p.m. Dr. Linda M. Thibodeau Department of Speech Communication The University of Texas at Austin Auditory enhancement and suppression have been suggested as possible mechanisms underlying one’s ability to understand speech. Using a forward-masking paradigm, enhancement and suppression effects were evaluated in two groups of normal-hearing persons who differed in…
Monday, October 29, 1990 4:00 p.m. Dr. Thomas Griffy Department of Physics The University of Texas at Austin Causality, the physical requirement that the effect not precede the cause, implies certain relations between the speed of propagation of a signal and its attenuation. These relations are called dispersion relations or Kramers-Kronig relations. This tutorial seminar…
Monday, October 22, 1990 4:00 p.m. E. T. Vishniac Department of Astronomy The University of Texas at Austin Accretion disks are extremely common objects, formed as the result of the collapse of gas onto a central object. The perturbation equations for such disks can be solved to yield a variety of waves. These waves are…
Monday, October 8, 1990 4:00 p.m. James TenCate, Michalakis Averkiou, and Chun-Fai Cheng Department of Mechanical Engineering The University of Texas at Austin and Applied Research Laboratories Over the past year or so, the acoustics group in the Mechanical Engineering Department has been putting together a water tank facility for ultrasonics on the 7th floor…
Monday, October 1, 1990 4:00 p.m. Assistant Professor Steve Morris Department of Petroleum Engineering The University of Texas at Austin Downhole multiphase flow measurements play an important role in the efficient recovery of hydrocarbon resources. Knowing what fluids are present at any depth in a well, and what their respective flow rates are at that…