bluuebunny/crossref_metadata_2025 huggingface dataset:
Progress Report on Automated Speaker-Recognition Systems
Authors: Kersta L. G.
Published: October 2005

This paper describes progress in the implementation of an automated speaker-verification system and a technique for codifying information contained within a voiced signal. The technique described is not dependent upon speaker amplitude variations and allows verification of speakers to be accomplished in real time. Subjective experiments of simulated automated systems utilizing spectrographic analysis and an adjustable filter with a decibel readout establishes the feasibility of such a codification process. The manual codification process resulted in a speaker-verification success score in excess of 60% when a single-word utterance was used. By further processing called “serial elimination,” several utterances are analyzed serially and result in scores of the order of 95% and greater. A completely automated version of the above-described simulated system employs a bank of narrow-band filters to separate the voiced signals into component spectral parameters. A feature extraction strategy called a “sliding window” is described, which was found to reduce effects of multiple-utterance “jitter.” In order to to reduce rejections of the desired speaker, his stored code is derived from the range of variance his utterances exhibit when collected from a succession of time-spaced utterances. With a serial elimination process, speaker-verification scores are comparable to those derived in the simulated system.
A Method or Speaker Verification
Authors: Doddington George R.
Published: October 2005

The speaker-verification problem is defined and contrasted with the speaker-identification problem. A speaker-verification experiment is performed using eight known speakers and 32 impostors. Formant frequencies, voicing pitch period, and speech energy—all as functions of time—are used in verification. Proper time normalization is shown to be an important factor in improving verification error performance. Nonlinear time normalization is performed by maximizing the correlation between sample and reference second-formant profiles through a piecewise linear continuous transformation of time. Average error rates after time normalization were: for pitch, 0.05; for formants, 0.04; for energy, 0.04; and over-all, 0.015. This over-all error rate is four times less than that obtained using only utterance endpoint alignment.
Near-Surface Ambient-Noise Correlation Measurements
Authors: Thorleifson J. M. , Jordan R. J.
Published: October 2005

Ambient-noise correlation measurements have been made in a deep ocean area with a vertical hydrophone array suspended at a depth of 100 ft. Spatial correlation coefficients were obtained for vertical hydrophone spacings of from 1 to 12.5 ft over the frequency range 100–2000 Hz and for sea states 2 and 4. The measured coefficients are compared to those obtained from theoretical models of ambient noise. The results indicate that below 200 Hz the noise field is mostly horizontal and is attributed to distant sources. Above this frequency, the field can be interpreted as arising from a uniform distribution of directional noise sources at the sea surface.
Adaptive Signal Detection with Finite Memory
Authors: Baxa E. G. , Nolte L. W.
Published: October 2005

In the Bayesian approach to signal-detection theory, infinite soft or changeable memory is tacitly assumed. Since an infinite memory is physically unrealizable, this study is concerned with formulating and optimizing a finite memory applicable to a large class of signal-detection problems. An optimum finite memory design is presented, assuming a priori that neither the eventual length nor the maximum length of the observation is known. The open-ended design is obtained and evaluated for the signal-known-exactly (SKE), the signal-known-except-amplitude (SKEA), and the M-ary signal-detection problems. Detection performance as a function of memory size is presented using the receiver operating characteristic (ROC) and plots of probability of decision error versus time. These results show the trade-off between memory size and processing time for the same detection performance. An important result is that a small finite memory detector with a memory size on the order of seven states, i.e., a three-bit computer word, yields detection performance very near that of the optimum infinite memory detector. [Research supported by Office of Naval Research, Acoustics Branch.]
Pipeline Sonar Development
Authors: Jones J. J.
Published: October 2005

Two years ago, Brown & Root surveyed the acoustic and magnetic fields with the idea of obtaining a “tool” to track pipelines on or beneath the ocean floor. It was imperative that the equipment acquired be capable of yielding high-resolution information as to depth, cover, and horizontal position of the line. Additionally, the surrounding bottom and sub-bottom structure information was desirable for determining loading and scouring characteristics. The results of the study were negative; however, we felt that a development program utilizing acoustics had a high probability of success. At this time, the developed equipment has been fabricated and is being readied for testing in the Gulf of Mexico. The finalized equipment configuration is basically a narrow beam sonar system, with a multiple element array, that is hydralically scanned at the rate of 30/sec. Owing to the required speed of data collection, it was decided to implement fiber-optic displays in a format that would allow for three-dimensional viewing of the bottom and sub-bottom strata by the operation on location. Additionally, the fiber-optic method allowed for direct digital printout of positioning information and depth on the sonar records, in real time, eliminating lengthy data reduction normally performed on shore.
Acoustic Imaging in a Borehole
Authors: Zemanek J.
Published: October 2005

An instrument called the Borehole Televiewer has been developed for making acoustic pictures of the walls of a borehole. Very often certain problems in exploration and production of oil can be solved from information gained by looking at the face of the borehole. Owing to the fact that the well is usually filled with an opaque liquid such as drilling mud or oil, optical devices (e.g., cameras or television) cannot be used. The Televiewer, using pulsed 2-mHz sound, scans the borehole wall. From the amplitude of the reflected signal a pictorial representation of the wall is made. The form of the picture is as if the well were vertically split in the magnetic north direction, unfolded and laid flat. Well features are reproduced in extraordinary detail on the resulting pictures. Azimuthal resolution is on the order of 132 in., which is unusual when one considers that the piezoelectric transducer is a disk 12 in. in diameter.
Field Applications of Resonant or Standing-Wave Systems in Heavy Industries
Authors: Bodine A. G.
Published: October 2005

High-specific-performance mechanical-inductive oscillators in matched combination with selected resonance modes of relatively large total systems can be arranged to produce simple and rugged machines having low losses at high power and which automatically maintain themselves within predetermined limits of operation. Widely varying field conditions, such as wide changes in lead impedance, can be automatically accommodated in the machine response by designing the resonator using test data which determine the impedance characteristic needed of the resonator while adapted to use the lockin characteristic of the inductive oscillator. Stress limitations and amplitude control can also be assuredly automatic under widely varying environments of load and operational monitoring (or lack thereof), by predetermining the frequency and power of the matched inductive oscillator and prime mover. Field machine examples are shown.
Review of Sonic Boom Generation Theory and Prediction Methods
Authors: Carlson H. W. , Maglieri D. J.
Published: October 2005

Within the past two decades the combined contributions of scientists and engineers in this country and abroad have resulted in development of systematic and reliable methods for the prediction of sonic-boom phenomena. The prediction techniques reviewed in the present paper permit the calculation of sonic booms produced by rather complex conventional supersonic aircraft designs performing level nonaccelerated flight in a quiet atmosphere. It has been found that the calculated characteristics for a quiet atmosphere are representative of nominal conditions in a statistical sense for a real atmosphere. Basic concepts of supersonic flow analysis for representation of an airplane as a linear distribution of disturbances and for determination of the resultant pressure field complete with shocks are outlined. Numerical techniques for implementation of the theory are discussed briefly and examples of the correlation of theory with experimental data from wind-tunnel and flight tests are presented. Special attention is given to presentation of a simplified method for rapid “first cut” estimation of farfield bow shock overpressure. Finally, some problems encountered in attempts at applying the prediction techniques for the near-field at high supersonic Mach numbers are recognized, and the need for further refinement of present techniques or the development of new systems is discussed.
Sonic Boom Minimization
Authors: Seebass R.
Published: October 2005

There have been many attempts to reduce or eliminate the sonic boom. For supersonic aircrafts such attempts fall into two categories: (1) aerodynamic minimums and (2) exotic configurations. In the first category, changes in entropy and the Bernoulli constant are neglected, and equivalent body shapes required to minimize the overpressure, the shock pressure rise, and the impulse are deduced. These results include the beneficial effects of atmospheric stratification. In the second category, the effective length of the aircraft is increased by modifying the Bernoulli constant a significant fraction of the flow past the aircraft. A figure of merit is introduced which makes it possible to judge the effectiveness of such schemes. Finally, the sonic boom reductions that can be achieved by hypersonic flight at high altitudes are summarized.
Sonic Boom Propagation in an Unsteady Atmosphere
Authors: Pierce Allan D. , Maglieri Dominic J.
Published: October 2005

A review is given of information obtained in recent years concerning the effects of atmospheric unsteadiness on sonic boom signatures. These effects include the observed random variations in boom overpressures from those expected for a stratified atmosphere, the anomalously large and variable risetimes, and the occurrence of spiked or rounded waveforms rather than the characteristic N waves. The extent of the variability in data recorded during actual flight tests is summarized in the form of histograms, representing experimentally obtained probability density functions. The physical mechanisms believed to be responsible for the variations and the anomalous features in the signatures are described. These include refraction and subsequent wavefront rippling by turbulence, the possible focusing or defocusing of rays, the formation of caustics and the phenomenon of wavefront folding, and diffraction. Recent statistical theories of shock propagation through a turbulent atmosphere proposed by Crow, Plotkin and by George, Pierce, and Horning are reviewed.
The Ultrasonic Bubble Chamber
Authors: Brown R. C. A. , Hilke H. J. , Jarman P. D.
Published: October 2005

Tracks from ionizing particles in liquid helium have been obtained at CERN using pulsed ultrasonic fields in the frequency range 100–400 kHz [R. C. A. Brown, H. J. Hilke, and A. H. Rogers, Nature 220, 1177–1178 (1968)]. However, with liquid hydrogen, ultrasonic techniques have so far only produced tracks when supplemented by some piston-produced expansion of the liquid [R. C. A. Brown, G. Harigel, and H. J. Hilke, Nucl. Instrum. Methods 82, 327–330 (1970)]. Experiments to define the optimum conditions for bubble growth and recompression in liquid helium have shown that a liquid-helium ultrasonic bubble chamber should be able to achieve a repetition rate of 100 Hz. Current developments are intended to produce a fast-cycling hydrogen bubble chamber sensitized purely by ultrasonic waves. A sound pressure amplitude of about 3 atm is required to do this, whereas only about 0.3 atm is needed for liquid helium.
Rapid Cycling and Sonic Bubble Chambers
Authors: Barney H. H. , St. Lorant S. J. , Rogers A. H.
Published: October 2005

Historically, bubble chambers have been expanded by either hydraulic or gas-actuated pistons or diaphragms. Such systems are easily capable of generating the necessary pressure drops (e.g., Δp pf 60 psi from a static level of 90 psi), even in chambers of 1 m3 volume or greater. Their chief limitation lies in the relatively low cycle rate (1–10 cps) inherent in such techniques. Various acoustical systems offer attractive alternatives. In particular, an electromagnetic driver (as used in vibration studies) has been tested as an expansion system on model liquid-hydrogen bubble chambers at SLAC, and a program to build a working chamber incorporating this technique is under way. The possibility of achieving the necessary expansion using standing sonic waves (frequencies from 180 to 8000 cps), and various means of generating such waves, are also being investigated.
Cavitation in Helium at Low Frequencies
Authors: Neppiras E. A. , Vroulis T. , Finch R. D.
Published: October 2005

Previous studies showed that cavitation noise and the half-order subharmonic occurred at much lower thresholds than required to produce macroscopic visible bubbles in the superfluid helium II. It might be supposed that this low “audible” threshold is associated with the presence of subvisible resonant bubbles. Accordingly experiments are in progress at lower frequencies in anticipation that any such bubbles will be larger in size with consequently less distinction between audible and visible thresholds. One investigation employed a sandwich-type transducer coupled to the liquid through a velocity transformer operating at 9.93 kHz. Measurements of particle velocity were made by including the transducer as one arm of a Wheatstone bridge and monitoring the off-balance voltage. Pressure thresholds could be deduced from this information assuming progressive wave radiation. In helium II, at a temperature of about 2.0°K, pressure amplitude thresholds were found to be as follows: for subharmonic generation 0.4 mbar; for white-noise generation, 3.4 mbar; and for visible bubble generation about 30 mbar; i.e., there was still a large difference between audible and visible thresholds. A device designed to operate around 100 Hz is presently under construction.
Microbubble Population Measurements Using Rectified Diffusion Caused Dispersion
Authors: Sachs Thomas D. , Slayton Peter W.
Published: October 2005

Decay times of 30 msec have been measured for microbubble populations repetitively grown in degassed water by bursts of 489-khz sound a few milliseconds long and of the order of 102 bars amplitude. The measurements were made by monitoring the differential phase shift of a pulsed low-amplitude sensing beam at two different times after the liquid through which it passes is perturbed by the 480-khz burst. The phase shifts were detected using a double balanced mixer and the sensing beam reference oscillator. The mixer output was then integrated during the time the sense burst was being received, the resulting integral was analog-to-digital converted, and then the appropriate differences taken digitally. The system was cycled 320 times for each measurement and digitally averaged. The differential velocity measurements were of the order of 2×10−2 cm/sec. The system noise level, including thermal shifts in the velocity, produced standard deviations in the values measured of less than 3×10−3 cm/sec. The resolution of the system was less than 1×10−6 cm/sec. [Work supported in part by the National Science Foundation.]
The Motion of Transient Cavities in an Acoustic Stationary Wave
Authors: Crum L. A. , Nordling D. A.
Published: October 2005

It is known that transient cavities, generated by cavitation in an acoustic stationary wave, travel at high velocities outward from the region of high acoustic pressure. An analysis of the motion of these cavities generated in a cylindrical resonator has been made. Cavity velocities, on the order of 100 cm/sec, were obtained by photographing the cavitation event under stroboscopic illumination. Owing to the short duration of the stroboscopic flash, considerable detail can be seen in the photographs of individual cavities moving outward from the acoustic pressure antinode. Acoustic pressure amplitudes were near but above threshold and varied from approximately 3 to 8 bars. The cavities varied in size, were roughly spherical in shape, and tended to break up as they collapsed. Some photographs show several tracks diverging from the same point, apparently originating simultaneously. It is found that if the cavities are treated as spherical bubbles, then the observed motion agrees roughly with that predicted analytically. [Work supported by the Office of Naval Research and the Naval Academy Research Council.]
Two Experiments on Pitch Perception
Authors: van den Brink G.
Published: October 2005

(A) Diplacusis of harmonic AM signals: Binaural diplacusis has been measured for harmonic three-component signals (amplitude modulated). The relative frequency difference necessary for equal pitch in both ears, plotted as a function of the modulation frequency, shows an irregular pattern, comparable with pure-tone diplacusis patterns [VAN DEN BRINK, G. (1970), “Experiments on Binaural Diplacusis and Tone Perception,” Symposium on Frequency Analysis and Periodicity Perception in Hearing, Driebergen, The Netherlands, 1969 (Sythoff's Publishing Cie, Leiden) (to be published)]. In all cases, the pitch of the signals corresponded with that of the common, though not presented, fundamental (residue pitch). The patterns, measured this way, appeared to be in good agreement with patterns obtained by averaging the diplacusis values for frequencies corresponding with the separate spectral components determining the pitch of a complex signal. This might mean that the origin of binaural diplacusis is not to be sought in a peripherally located mechanism, but rather in a higher center. (B) Pitch of inharmonic AM signals: Monaural matching of inharmonic AM signals with harmonic signals gives direct quantitative information of pitch deviations, found with regard to the time-fine structure theory [SCHOUTEN, J. F., RITSMA, R. J., AND CARDOZO, B. L. (1962). “The Pitch of the Residue,” J. Acoust. Soc. Amer. 34, 1418.] The results show no deviation for signals with a small rate of inharmonicity, but progressively increasing deviations for greater rates of inharmonicity. It also was found that the deviations decrease with decreasing intensity and with decreasing modulation depth. Our findings suggest that the deviations are due to neural interaction mechanisms. Efforts to describe pitch mechanisms with simple mathematical formulas are therefore not likely to be successful.
Pitch Memory for Two Tones
Authors: Elliott Lois L.
Published: October 2005

Pitch memory for two successive tones with simple (musical third or fifth) or complex frequency ratio was studied in a recognition procedure. The 6-sec interval between target tones and comparison tones was either silent or contained two intervening tones. Pitch DL for each of two tones is about 1.5–2.0 times larger than for one tone. The DL for pairs of tones with complex frequency ratios is, under some circumstances, larger than that for pairs of tones with simple ratios. For “good pitch discriminators,” the task must become more difficult before ratio complexity affects performance than is true for “poor pitch discriminators.” At least two skill components, “frequency analyzing power” and memory, are present in these tasks and consistent individual differences occur for both. [Supported by an NINDS grant to CID.]
Comparison of Performance in Three Paradigms for the Study of Intensity Discrimination
Authors: Viemeister N. F.
Published: October 2005

Performances in the following auditory intensity discrimination paradigms were compared: (1) 2IFC; (2)single-interval rating with an intensity cue preceding each observation interval; (3) single-interval rating with no cue. ROC curves obtained in the single-interval tasks can be well fitted by assuming that the underlying distributions are both Gaussian and have equal variance. No large difference was observed between performance in the cue and the no-cue conditions. The normalized separation of the means of the decision variable for 2IFC was approximately twice the corresponding estimate for the single-interval conditions, i.e., d2 = 1.91d1. This is consistent with the hypothesis that the observer bases his decisions on the difference between the observed input and a noisy stored reference in certain intensity discrimination tasks. This hypothesis can be incorporated easily into most models of intensity discrimination and can account for the familiar result that d2 = √d1 for simple detection. [Supported by an NIH Predoctoral Fellowship and by the Information Sciences Directorate, Air Force Office of Scientific Research.]
Signal Ensemble and Intensive Discrimination
Authors: Bilger R. C. , Wang M. D. , Jesteadt W. H.
Published: October 2005

Intensive DLs were obtained for three listeners as a function of carrier level for four signal ensembles. The intensive difference signal was defined either by amplitude modulation of the carrier by an 8-Hz sinusoid or by addition of a 500-msec intensive increment to the carrier. Carrier level was defined either by a continuous tone or by a 500-msec pulsed tone at 1000 Hz. An adaptive sequential procedure, incorporating 4IFC method, was used in estimating thresholds. All except the steady-state, pulsed-carrier ensemble showed the improvement in discrimination usually associated with ΔI/I. DLs for the continuous carrier tended to be smaller than those for pulsed carrier. Also, detection was more acute for the AM signal than for the fixed difference in intensity, except near threshold where this relationship reversed itself. The atypical magnitude and level dependence of DLs for the pulsed-carrier steady-state ensemble can be related to other aspects of auditory perception.
Frequency Discrimination in Noise
Authors: Javel E. R. , Jesteadt W. H. , Bilger R. C.
Published: October 2005

Frequency DLs were obtained near masked threshold (1–15 dB SL) at 250, 1000, and 4000 Hz. Three spectrum levels (31.5, 51.5, and 71.5 dB) were used. An adaptive sequential procedure based on 4IFC was used in estimating ΔF. Also, two signal modes were used. In one, the pulsed tone presented during the “signal interval” was frequency modulated. In the other, the pulsed tone presented during the “signal interval” was a steady, but different, frequency. Characteristic improvement was seen at all frequencies when ΔF was plotted as a function of sensation level. At 4000 Hz, however, a significant “noise-level” effect was noted, in which discrimination at the 51.5-dB spectrum level (band level of 86 dB) was poorer than that for 31.5 and 71.5 dB. This “noise-level” effect was essentially the same for both modes of signal presentation. While this effect is difficult to explain in psychophysical terms, the literature on physiological acoustics offers some promise of accounting for it.
Response and Acoustic Radiation of Multimodal Systems; Modal Grouping and the Design of Experiments
Authors: Berkman Frank , Kerwin Edward M.
Published: October 2005

The response and acoustic radiation of multimodal structures are often discussed in qualitative terms. For example, the modes of a flat plate are classified as “surface,” “edge,” and “corner,” with respectively decreasing radiation loss factors. Thus the differences—assumed large—among these modes might be evident in experimental data. To assess this expectation we explore analytically the following questions: “Can a laboratory experiment be designed to demonstrate the existence and predicted behavior of these classes of modes? Specifically, can certain expected asymptotes and ‘break points’ be identified on radiation-versus-response curves where the internal damping is varied to generate the curve?” Our answer is typically “No” because (a) the effect of relative numbers of modes in the various classifications, often ignored in qualitative discussions, tends to counteract the effect of the differences in radiation losses; “b” the required range of internal loss factor is impractically large; (c) the asymptotes are not easily identifiable because the response and radiation do not vary rapidly enough with internal losses, relative to the spread in radiation losses between classes. Thus, although the modal classifications are useful as quantitative analytical tools, the differences in modal characteristics are not necessarily obvious in the behavior of multimodal systems. The system investigated is a baffled, simply supported, heavily fluid-loaded rectangular plate driven with a random point force.
Integral Equation Techniques for Structural-Acoustic Interaction
Authors: Wilkinson J. P. D. , Liu H. K.
Published: October 2005

A method is presented for the numerical study of the interaction of elastic bodies and acoustic fields. It is based on an integral equation technique wherein a sheet of acoustic sources and a sheet of forces are spread over the body surface. Their strengths are adjusted so that the boundary conditions are satisfied at the fluid-solid interface. Because the calculation involves only a description of the body surface, it offers a more rapid numerical process than the more usual finite element calculations, where equations of motion must be developed for all points within the interior of the body as well.
Scattering by an Irregular Blob of One Fluid Embedded in Another
Authors: Hudimac A. A. , Sears M.
Published: October 2005

The wavefield and its normal derivative on one of the sides of the closed surface of separation is determined by dual integral equations. One of these is straightforward. The other, involving the normal derivative of a Helmholtz surface integral, does not exist unless a limiting form is taken. An approximate numerical solution is obtained by dividing the surface of integration into patches and approximating the integrals thereon. The scattered wavefield or the wavefield in the blob can then be obtained as finite-sum approximations of the corresponding Helmholtz integral formulas.
Reflection of Sound by Air-Backed Plates in Water
Authors: Barss Walter M.
Published: October 2005

Sound pulses are being reflected from air-backed plates in water, in order to simulate the reverberation observed when acoustic navigating equipment is used under a floating layer of sea ice. The techniques for generating sound pulses and detecting the reflected pulses have been greatly improved since they were described at the Cleveland meeting. The signal frequencies now extend from 100 to 3000 kHz (ka from about 2 to 60 for plates of typical thickness). The intensity of reflected pulses is displayed qualitatively, as a function of both angle and frequency, and the data are also recorded digitally on magnetic tape for quantitative processing by computer.
Statistics of the Sound Field of a Source above a Rough Imperfectly Reflecting Surface
Authors: Hardin J. C. , Brown T. J.
Published: October 2005

A theoretical analysis of the sound field due to a sinusoidal source located above a rough reflecting surface with variable admittance is developed. Both the elevation and the admittance of the surface are represented by isotropic random processes. The Helmholtz solution is employed with the boundary conditions approximated by the field which would be present on the local tangent plane. This yields a formulation in which contributions to the solution from variations in surface elevation, slopes, and admittance are clearly evident. Moment properties of the field are then obtained in terms of the first-order and joint characteristic functions of the surface and the autocorrelation of the admittance. In certain instances, asymptotic expansions of the integrals representing the mean field yield simple formulas involving tabulated functions. The results are of interest in connection with ground effects on aircraft noise measurement.
Human Response to Sonic Boom in the Laboratory and the Community
Authors: von Gierke H. E. , Nixon Charles W.
Published: October 2005

The bases for present-day estimates regarding man's understanding of and response to sonic booms may be found in various observations, overflight programs, and in experimental laboratory and field studies which are reviewed in this paper. Loudness, startle, annoyance, performance, and sleep responses are related to the overpressure, duration, and pressure-time function of individual sonic booms. The complex reactions of individuals, groups, and communities exposed to sonic booms of varied magnitude and frequency of occurrence are also discussed. Experiments are described that show that even sonic booms of maximum intensity presently feasible have not produced any observable direct medical injury. The integrated body of results of recent physiological, psychoacoustic, behavioral, and sociological studies from various countries provides estimates of the effects and acceptability of regular, frequent supersonic commercial overland flights. These data are also considered relative to aircraft noise pollution in general and of potential certification of aircraft with respect to sonic boom.
Growth, Pulsation, and Collapse of a Gas-Filled Cavitation Bubble
Authors: Flynn H. G.
Published: October 2005

A mathematical formalism has been developed for studying the dynamics of small gas-filled cavities in liquids under the influence of acoustic pressure fields. The formalism takes into account the effects of compressibility and heat conduction within the cavity, of compressibility, heat conduction, and viscosity in the surrounding liquid, and of the surface tension of the interface. The formalism consists of a set of algebraic, differential, and integral equations, and computer solutions of this set of equations have been obtained. The results of these calculations will be used to discuss the growth of cavities from some equilibrium state, the free pulsations of cavities, and the collapse of cavities. The main objective will be to provide insight of the relative importance of such effects as compressibility, heat conduction, viscosity, and surface tension on the motion of cavities. [The work described was carried out in cooperation with the Acoustics Research Laboratory at Harvard University and was supported by the Acoustics Programs of the Office of Naval Research under contract with the University of Rochester and with Harvard University.]
Cavitation from Stable Bubbles
Authors: Nyborg Wesley L.
Published: October 2005

It is desirable for both scientific and practical reasons to improve control of sonic cavitation. A problem in doing this is to provide gas bubbles in specified numbers, sizes, and configurations. Another is to prevent onset of chaotic surface waves with their associated complications. Various approaches to these problems have been made recently with encouraging results. Thus Neppiras was able to study subharmonic generation from stable bubbles in viscous glycerine-water mixtures, while Saksena and the author observed sonoluminescence under similar conditions. With another arrangement Rooney has been able to carry out sonication of small quantities of biological suspensions by means of a single stable bubble. Under such controlled conditions, it is possible to be selective about the action evoked by sound. Thus the threshold for sonoluminescence, emulsification, and polymer degradation are in general different. These thresholds can be accounted for, with varying degrees of accuracy, from theory for chemical kinetics (in connection with sonoluminescence) and for acoustic streaming (in connection with emulsification and polymer degradation).
Sonoluminescence and the Acoustic Cavitation of Water
Authors: Taylor K. J.
Published: October 2005

The emission of sonoluminescence from aqueous solutions cavitated at 16 and 500 kHz is discussed in terms of the bubble motion with which it is associated and the mechanism by which the light is produced. It is shown from measurements of the phases of the sound pressure cycle at which the sonoluminescence flashes occur that bubble nuclei must grow to over half their resonant size before being capable of imploding to produce a sonoluminescence flash and that the secondary flash is probably due to a bubble rebound. Spectra of the sonoluminescence from different solutions show continua of various shapes, OH bands, and, in cases where there are salts in solution, spectral lines which may be quenched by the presence of some dissolved gases. From these data a model is postulated which suggests that part of the light emitted is due to an incandescence of the bubble contents and part to chemiluminescent reactions within the bubble. It is shown that no feature of the spectrum can give much useful information about conditions within the bubble during its implosion, although other authors have suggested the contrary.
Cavitation, “Pure” and Simple
Authors: Apfel Robert E.
Published: October 2005

Two areas of capitation research have met with limited success until recently: (1) the measurement of the strength or cavitation threshold of pure (mote-free) liquids; and (2) the prediction of the threshold of liquids known to be “impure.” Advances in these areas are reviewed and new results are reported. The influence of mote size and mote wetability on the cavitation threshold has been studied theoretically [R. Apfel, J. Acoust. Soc. Amer. (to be published)]. Results of this work bring some semblance of order to a wide variety of cavitation observations. By minimizing the number of motes in the liquid sample and by isolating the sample from solid container surfaces, it is possible to measure the strength of pure liquids. This has been accomplished by testing small filtered droplets of the sample suspended in an “inert” host liquid. Furthermore, the tests have been performed at temperatures at which the sample has undergone significant super heating; under this condition, the predicted tensile stresses are low enough to be accessible experimentally. This technique [R. Apfel, J. Acoust. Soc. Amer. (to be published)] has been modified with the intention of studying the liquid-to-solid phase transition. [Work supported by the Office of Naval Research.]
An Instrument for Detecting and Analyzing Microbubbles
Authors: Turner William R.
Published: October 2005

Final objective for the acoustical microbubble spectrum analyzer is the in situ detection and analysis of microbubble populations in the ocean by measuring the differential ultrasonic velocity and attenuation between a sea water sample and a reference liquid over a continuous frequency range from 0.1 to 5.0 MHz. Ultrasonic waveguides retain these liquids. Reverberation is suppressed by using an accurate continuous frequency ramp over the range, together with frequency processing of the difference between the waveguide input and output signals. The resultant signals are logarithmically compressed. A differential attenuation output is derived from the envelope functions, and a differential velocity, from the wave periods. Several critical state-of-the-art problems have been solved, but further developmental work remains. The differential attenuation response is now sufficiently sensitive for the observation of certain microbubble phenomena. [This work supported by the Office of Naval Research.]
Effect of Amplitude on Auditory Filter Shape
Authors: Patterson Roy D.
Published: October 2005

The detectability of a pulsed sinusoid was measured as a function of its distance, Δf, from a broad band of noise having very sharp skirts. Noise-power density, N0, in the passband was essentially constant. The function relating masked threshold to Δf was determined, for a wide range of frequencies, at three levels of noise-power density )N0 = 25, 40, 55 dB SPL(. When the noise band is above the sinusoid, in frequency, the shape of the masked threshold curves is independent of N0, that is, the curves are parallel. However, when the noise band is below the sinusoid, and increase in N0 from 40 to 55 dB leads to a very pronounced flattening of the curve. These data suggest that the auditory filter broadens with increasing amplitude above N0 = 40 dB, and that this broadening is entirely due to a decrease in the off-band attenuation rate on the low side of the auditory filter. [Research supported by the National Institutes of Health, Public Health Service, U. S. Department of Health, Education, and Welfare, and by a research grant awarded to to the Center for Human Information Processing.]
Probability Distribution of Some Psychophysical Latency Intervals: A Theoretical Study
Authors: Divenvi P. L. , Wyss C. R.
Published: October 2005

In repeated independent trials, an ideal device integrates the energy of a sinusoidal signal embedded in band-limited Gaussian white noise. Whenever the energy accumulated in the integrator reaches a fixed threshold value, a pulse is triggered. The latency of this pulse, with respect to the on-set of the input, will be a random variable whose distribution is an inverse function of the noncentral chi-squared distribution. Three parameters affect the latency: signal-to-noise ratio, threshold level, and noise bandwidth. For different threshold levels, families of probability density functions are skewed; both their means and variances increase with decreasing signal-to-noise ratio and with increasing threshold; the noise bandwidth acts as a scalar of the coordinate system.
Rating Method for the Study of Detection without Defined Observation Intervals
Authors: Watson Charles S. , Wroton Henry W.
Published: October 2005

Watson and Nichols [J. Acoust. Soc. Amer. 39, 1247, 1966(a)] described an experiment in which 10 tonal signals and 10 instances of noise alone were distributed randomly over the course of 5-min listening periods. Although listeners responded at low rates, distributions of response latencies were estimated for signals plus noise and for noise alone, and from these distributions values of the detectability index, d′, were calculated. We now find that listeners can be trained to respond very frequently in this task when they are allowed to use low-confidence ratings for faint signal-like events in the noise background. Relations between ratings and the probability that a response is correct, relations between confidence level and response latency, and also the slopes of rating ROC curves (plotted on normal-normal coordinates) are all similar to those from experiments with defined observation intervals.
Detection, Discrimination, and Temporal Integration of Near Threshold Levels
Authors: Clarke F. R. , Bell W.
Published: October 2005

These experiments explored the empirical relations among growth of detection as a function of SPL, amplitude discrimination performance, and temporal integration. To a first order of approximation the results were as follows: ROC curves in quiet were linear on normal-normal coordinates, the slope of the psychometric function did not vary as a function of duration, the slope of the psychometric function was inversely proportional to the size of the difference limen, and amount of temporal integration was inversely related to the slope of the psychometric function. Some theoretical considerations relating to this last finding will be discussed.
Pip Detection in the Presence of a 50-Hz Signal during Monotic and Dichotic Presentations
Authors: Brandy W. T. , Cooper W. A.
Published: October 2005

Eight trained normal-hearing male adults served as observers in this counter-balanced YES-NO study. Equivalent-level pips were presented to the right ear of half the observers and to the left ear of the others during all reference, control, and experimental conditions. For the experimental runs, the pips were presented at 90° and 270° re an on-going 50-Hz sinusoid. The pips and sinusoid were presented monotically and dichotically to each observer. Four of the observers received the sinusoid at −10 dB SL and four received it at 5 dB SL. Essentially equal amounts of sensitization were observed during the −10 dB SL and 5 dB SL 90° monotic conditions. This finding corroborates earlier reports. Neither sensitization nor desensitization was observed during the −10 dB SL and 5 dB SL 270° monotic conditions. Essentially equal and remarkable amounts of desensitization were observed during the −10 dB SL and 5 dB SL 90° and 270° dichotic conditions. There was no significant difference in performance between the right- and the left-ear groups of observers, but the right-ear group had somewhat higher detectability scores in all but one of the conditions.
Steady-State Whirl of a Long Eccentric Shaft under Variable Tension Rotating in a Viscous Medium
Authors: Michalopoulos C. D. , Muster D.
Published: October 2005

The problem of whipping of an eccentric, long circular shaft under linearly varying tension rotating in a fluid medium is investigated within linear theory. In view of the great lengths under consideration, the bending stiffness is assumed negligible. Internal damping is neglected and the external damping is assumed viscous. The mass eccentricity is assumed to be a deterministic function of the axial coordinate. Only steady-state conditions are considered. The deflection of the shaft is obtained by finite Hankel transforms, and the bending stresses are subsequently determined approximately from the curvature of the deflection curve. Numerical results are given in graphical form for a shaft with a pulse-type eccentricity function in one plane for several values of speed of rotation and tension at the lower end.
Driven Nonlinear Oscillations of a String
Authors: Eller Anthony I.
Published: October 2005

Because of nonlinearities, the forced oscillations of a string, moving in a single plane, become unstable when the string is driven with sufficient amplitude near resonance. This paper describes the experimental conditions under which forced string oscillations in a vertical plane become unstable. It is found that planar oscillations become unstable in two different ways. One instability is triggered by a spontaneous growth or decrease in the amplitude of the driven vertical motion. The other instability is triggered by a spontaneous growth of a horizontal component of motion, thus leading to a whirling or nonplanar motion of the string. The conditions under which each instability occurs are distinct. These experimental observations agree with the conclusions by Anand [J. Acoust. Soc. Amer. 46, 667–677 (1969)], based on a theoretical analysis. This paper also describes the response of the nonplanar mode of oscillation. It is found for certain conditions that the vertical amplitude of oscillation decreases as the driving signal is increased.
On the Utilization of a Flexible Bar as a Continuous Spatial Filter
Authors: Lambert R. F. , Aupperle F. A.
Published: October 2005

In order to determine empirically the wavenumber-frequency spectra of the wall pressure fluctuations beneath a turbulent boundary layer at nonconvective wavenumbers, a spatial filter with high wavenumber resolution is necessary. Such a filter can be realized by using a continuous system such as a flexible bar or by using a discrete array of finite-sized transducers. The bar offers the advantage that high wavenumber resolution can be achieved without the use of the elaborate equipment necessary for the transducer arrays. In order to use the bar as a spatial filter all that is required is a measurement of the modal displacement response at some spatial position. In this paper, the theoretical formulation of the bar as a continuous spatial filter is developed. Calibration procedures and measurement problems such as those associated with vibrational noise are discussed. Finally, measurements of the low-wavenumber (nonconvective) spectra of the wall pressure fluctuations obtained by using the bar as a spatial filter are reported. One important result of this study is that it demonstrates that the primary wavenumbers associated with the pressure fluctuations contributing to the bar response are not the convective wavenumbers. This implies that Corcos's model, which has been empirically verified only for wavenumbers near the convective wavenumbers [D. M. Chase, J. Acoust. Soc. Amer. 46, 1350–1365 (1969)], may not be adequate for predicting panel response. The measured low-wavenumber (nonconvective) spectra indicate the limitations of Corcos' model in this region. [Work supported by grant from the National Aeronautics and Space Administration.]
Analysis of Connected Continuous Structures Using Receptances
Authors: Faulkner L. L. , Hamilton J. F.
Published: October 2005

A method for the analysis of connected beam, ring, plate, and shell structures has been investigated, which results in an eigenvalue formulation of the combined system. The method consists of applying an equal and opposite force at the interface boundaries of the connected continuous elements. With proper spatial and time dependance, the system natural frequencies and mode shapes can be formulated by extending the method of Bishop and Johnson to receptances which are a function of the connecting boundary coordinate. To illustrate this method, the resonant frequencies and mode shapes have been computed for a simply supported shell with a stiffening ring, a simply supported shell with a stiffening rib, and a simply supported shell with circular end plates and a stiffening ring. This method gives a simple frequency equation and a convenient formulation for the mode shape.
On the Parametric Resonance of a Cylindrical Shell Subjected to a Periodic Axial Load
Authors: Koval L. R.
Published: October 2005

The dynamic stability of thin-walled circular cylindrical shell is studied for the case of periodic axial load. In computing the internal membrane stress induced by the axial pressures, the cylinder is assumed to act as a longitudinal bar. The internal membrane stress is computed by considering the shell to be a longitudinal rod with axial inertia terms included. Hence, the internal axial coordinate as well as with time and to include the resonances of the cylinder acting as a longitudinal rod. The problem under study is to determine the stability of the flexural motions of the shell oscillating about this inextensional mode. The shell motion is represented by Donnell's equations. A study of the solutions of these equations reveals parametric resonance of the well-known type and a second parametric resonance which appears to be new. The latter includes the combination resonance between two modes having the same modal pattern, and also between two modes having different modal patterns. In particular, this includes combination resonance between two transverse modes having a different number of axial half waves. This result is believed to be new and is considered the principal result of the study being described. It is only obtained when axial inertia is included in computing the axial membrane stress. It is found that combination resonance does not exist between modes having a different number of circumferential waves. The two modes must have the same number of axial waves. An estimate is given for the width of the unstable regions, and numerical results are presented. The extension to a shell having the effects of rotatory inertia and shear deformation is briefly discussed.