bluuebunny/crossref_metadata_2025 huggingface dataset:
Responses of gray whales, Eschrichtius robustus, to noise
Authors: Dahlheim Marilyn E.
Published: October 2005

Responses of gray whales to increased levels of noise were documented during playback experiments. Nine sound parameters were compared between control and experimental conditions: call rates, call types, frequency range (Hz), emphasized frequencies (Hz), received levels of sound (dB re: 1 μPa), call duration (s), calls exhibiting frequency modulation, pulses per series, and signal repetition rates. Whale surface behavior (i.e., dive durations, movements, and abundance) was also investigated. Analyses yielded: a description of call types; a characterization of acoustical habitats; and a determination of relationships between whale calls and habitats; and a determination of relationships between whale calls and habitats. Gray whales employed multiple behavioral strategies (e.g., modification of calling to optimize signal transmission and reception, movement out of the study area, etc.) to circumvent increased levels of noise in their environment. Responses varied with sound source and may also differ with geographical range and/or general behavior.
Application of multilayered structure for flow noise reduction
Authors: Ko Sung H.
Published: October 2005

Turbulent boundary layer pressure fluctuations can be reduced by filtering of its wave-number response with either a finite hydrophone or a hydrophone array, or by filtering the wave-number response through a layer (layers) of elastomer. The elastomer layer is frequently called an outer decoupler and the multilayered structure is a generalized outer decoupler. In general practice, hydrophone arrays are embedded within the outer decoupler to reduce the turbulent boundary layer pressure fluctuations and then mounted to an elastic structure. The analysis of a multilayered structure is presented here to evaluate the transfer function, which is a measure of wave-number filtering through an outer decoupler. The front of the first layer is exposed to turbulent flow and the back of the last layer is in contact with static air. The results presented here are the numerically calculated transfer functions and noise reductions achieved by various layers of elastomer mounted on a steel plate.
The prediction of echoes from underwater structures in the time-frequency domain
Authors: Gaunaurd G. , Strifors H.
Published: October 2005

An earlier study [J. Acoust. Soc. Am. 93, 2412 (A) (1993)] of echoes from submerged elastic shells in the combined time-frequency (t-f) domain is continued. Wigner and pseudo-Wigner distributions as well as time-windowed Fourier transforms are used [cf. L. Cohen, Proc. IEEE 77, 941 (1989)]. These distributions extract from the echoes the time evolution of the target resonances that may be present in the frequency band of operation. Selecting suitable carrier frequencies for the incident pulses and appropriate spectral windows, it is possible to produce (t-f) displays linking resonance features to specific target characteristics. It becomes clear that this type of display is helpful in the processing of the echoes, and in the identification of the scatterer’s material properties and geometrical shape. Broader/narrower time windows control the amount of detail in the resulting (t-f) plots, which can be adjusted at will. This is illustrated with examples exhibiting results in a colorized three-dimensional format as beautiful as practical and informative. These examples include the use of various realistic incident pulses, targets, and viewing windows that highlight the target-ID capability of the approach.
Time, frequency, and thickness analysis of monostatic scattering from an infinite steel cylindrical shell immersed in water
Authors: Yoder Timothy J. , Dragonette Louis R. , Gaumond Charles
Published: October 2005

The monostatic scattering for an infinite cylindrical steel shell is analyzed for frequencies up to ka=10.0. The shell thickness is varied from h/a=0.001 to h/a=0.999. The time, frequency, and thickness dependence of the scattering is graphically analyzed to determine the physical process(es) responsible for the scattering. This analysis reveals the following processes: (a) The Lamb wave circumnavigating the cylinder; (b) a 180-deg phase shift in the specular scattering as the shell becomes thick; (c) the coincidence frequency of the flexural waves with the radiation medium; (d) a drastic decrease in the ‘‘Q’’ of the modes supporting the flexural waves caused when the circumnavigating flexural waves begin to radiate efficiently; (e) the onset of the creeping waves as the shell becomes thick; (f) the transition of flexural/Lamb wave behavior to Rayleigh wave behavior as the shell becomes a solid cylinder; (g) cancellation of the monopole and dipole modes for frequencies less than ka=3 occurring at thickness h/a=0.05; (h) the poles of the normal mode series solution coinciding with the highlights seen in the frequency domain.
Time-frequency representation of scattering from a target in a bounded medium
Authors: Sarkissian Angie , Gaumond Charles F. , Yoder Timothy J.
Published: October 2005

Time-frequency representations applied to target scattering enable one to observe target characteristics that are of particular interest in inverse scattering problems. In this work such representations are extended to targets placed in a shallow water environment where target characteristics as well as shallow water characteristics appear in the time-frequency domain. The Gabor transformation is applied to scattering from an elastic shell placed in a bounded medium to display the combination of the waveguide effects (shallow water propagation) and the target effects (elastic wave propagation). The use of such representations for classification purposes is discussed.
A spectral description for the effects of multiple point masses in fluid-loaded plates
Authors: Cunefare Kenneth A. , Ginsberg Jerry H. , Babish John
Published: October 2005

The wave-number-based formulation of the surface variational principle describes the surface pressure and displacement as a comparatively small set of interacting waves. It enables one to pose questions of parametric sensitivity from a global perspective. A two-dimensional problem of an elastic plate in an infinite baffle with pinned boundary conditions is considered. A series of line masses attached to the plate, at regular and irregular spacings is considered. The specific mass distribution is replaced in the SVP formulation by an arbitrary continuous distribution along the length of the plate. The functional form of this distribution is described using a spectral Fourier series, whose ascending orders represent successive stages in refinement of the scale to which a model describes inertial effects. The excitation applied to the plate is taken as a concentrated harmonic force. With the excitation held fixed, the influence of each spectral component of inertial distribution on the surface response and radiated power are assessed. Evaluations carried out for a range of frequencies shed light on how small scale inertial heterogeneities can influence macroscopic radiation features.
The exterior acoustic modes of structures
Authors: Curry Noelle , Cunefare Kenneth A.
Published: October 2005

The use of a modal-style approach for the analysis of the exterior radiation characteristics of structures continues to receive increasing attention. This approach generally seeks to find a set of orthogonal functions, or acoustic modes, that diagonalize a radiation operator in the exterior domain of an extended radiator. These acoustic modes are found through an eigenfunction/eigenvector analysis or singular value decomposition analysis of the radiation operator. The eigenvalue or singular value associated with a given mode is directly proportional to the radiation efficiency of that mode. Here, the frequency dependency of the acoustic modes of a baffled beam is examined. Further, the dependency of the radiation efficiencies and mode shapes on the number of degrees of freedom permitted in the derivation of the radiation operator is investigated. It is demonstrated that the accuracy of the acoustic modal representation depends on the number of degrees of freedom permitted in the derivation of the radiation operator. The most efficient acoustic modes are least sensitive to increasing degrees of freedom. The least efficient acoustic modes are most sensitive to changes in degrees of freedom. This behavior has significant impact on applications of the exterior acoustic modal approach that seek to exploit the least efficient modes.
Adaptive control of bending wave intensity in a finite beam
Authors: Swanson David C. , Gentry Cassandra , Hayek Sabih I. , Sommerfeldt Scott D.
Published: October 2005

Adaptive control of the bending wave field in a finite beam is simulated using a classical Euler–Bernoulli analytical model and a dual-actuator filtered-x feedforward controller. Three different intensity-based error signal strategies are compared for multiple locations on the beam in and out of the near field of the actuators. The goal is to actively minimize the propagating bending wave power where the five-element error sensor array may be located in the near field of the actuators. Since the error array must be effective in the near field, the idea of simultaneously minimizing all five accelerometer signals was rejected. Reults from using an instantaneous intensity error estimate were ineffective due to the nonlinearity in the adaptive control error gradient. Results from minimizing the intensity (rather than intensity-squared) were acceptable and consistent with the experimental results of Sommerfeldt [Sommerfeldt etal., J. Acoust. Soc. Am. 93, 2370 (A) (1993)]. A new error method based on an intensity transfer function plant also produced acceptable simulation results. [Work supported by the GEM Fellowship Program.]
Imaging techniques for the larynx and vocal tract
Authors: Hirose Hajime
Published: October 2005

A recently developed method of digitally imaging vocal fold vibration was applied for the analysis of the nature of diplophonia, which is defined as the simultaneous production by the voice of two separate tones. In the present system, a specially designed tele-endoscope is attached to a single-lens reflex camera that houses a solid-state sensor at the position of the film plate. when the shutter is released, an image scan is made under computer control, and image signals are stored in the image memory. The image can be reproduced and displayed for later analysis. In the case of diplophonia, it was revealed that there is an asymmetry in the vibratory frequency of the left and right vocal folds associated with quasiperiodic variation in the speech waveform. As for the imaging technique for the vocal tract, a preliminary result of observation of the inner structure of the tongue using tagging snapshot MRI will be presented.
Man-made noise in shallow water
Authors: Mitchell Stephen K.
Published: October 2005

In many important shallow water areas, merchant shipping, fishing, or seismic exploration activities are a prominent feature. In such regions, the ambient noise levels in the frequency range from approximately 10 Hz to 1 kHz are generally dominated by sounds related to these activities. Ambient noise levels are generally much higher than those typical of deep ocean regions; omnidirectional and beam levels show considerable temporal variability as noise sources move and change their activities. Noise data from measurements in shallow water regions will be summarized. In addition, the interaction between source characteristics, shipping densities and traffic patterns, propagation characteristics, and ambient noise statistics will be discussed. [This work is supported by the Office of Naval Research, Code 234, under block RL3B.]
The source pressure field arising from wave–wave interactions in shallow-water environments
Authors: Kibblewhite A. C. , Wu C. Y.
Published: October 2005

Theoretical treatment of the noise source induced by wave–wave interactions have been traditionally based upon the assumption of an infinitely deep ocean. Growing interest in the application of the wave-induced pressure field as an acoustic source in the determination of the sub-bottom geoacoustic structure in shallow-water areas calls for a study of the influence of water depth on the physical processes involved. This paper presents some results based on such an extension. It shows how the depth-dependent surface-wave dispersion relation and porosity in the upper layers effect the spectral properties of the resulting ULF noise field in shallow-water environments. [Work supported by ONR.]
Accurate finite element methods for fluid-loaded plates
Authors: Grosh Karl , Pinsky Peter M.
Published: October 2005

The design and analysis of new finite element methods for the steady-state response of fluid-loaded Reissner–Mindlin plates is presented. In this study, new methods are developed that are more accurate than standard finite element methods in their ability to represent wave propagation for coupled problems in structural acoustics. Generalized Galerkin least-squares (GGLS) finite element methods have been employed previously to enhance the accuracy of the finite element approximation for the uncoupled structural problem [K. Grosh and P. M. Pinsky, in Proc. SecondInt. Conf. Math. andNumer. AspectsofWavePropagation, edited by R. Kleinman etal. (June 1993)] and the uncoupled acoustic problem [I. Harari and T. J. R. Hughes, Comput. Methods Appl. Mech. Eng. 87 (1991)]. Complex wave-number dispersion analysis is used both to design the new methods and characterize their accuracy. Results comparing the finite element dispersion relations to the analytic dispersion relations for the fluid-loaded Reissner–Mindlin plate demonstrate the enhanced accuracy of these new GGLS methods over the standard Galerkin finite element implementation.
Direct evidence for automatic gain control in the cochlea
Authors: Zwislocki J. J. , Chatterjee M.
Published: October 2005

Compression of the input/output functions of auditory nerve fibers was ascribed to automatic gain control by Rose and his associates many years ago. It was ascribed to synaptic processes [C. D. Geisler and S. Greenberg, J. Acoust. Soc. Am. 80, 1352–1363 (1986)]. But compression is known to take place in the cochlea, as has been documented at the basilar membrane and hair cell levels. By comparing measured waveform distortion and the size of the second harmonic to those predicted from the input/output functions of Hensen’s cells, it is demonstrated that the cochlear compression is due to automatic gain control at least up to a sound pressure level of 70 dB in Mongolian gerbils. Strong compression has been found at levels as low as 20 dB SPL. Since the response magnitude of Hensen’s cells has been shown by the present authors and others to be directly proportional to that of the outer hair cells, this demonstration should be applicable to the hair cells themselves. The almost complete lack of waveform distortion was present independent of frequency distance from CF and could not have been caused by spectral filtering. [Work supported by NIDCD Grant No. DC00074.]
The roles of parametric demodulation, rectifying demodulation, and coherent demodulation in human amplitude-modulated ultrasonic hearing
Authors: Zeng Shengke , Beard Richard B.
Published: October 2005

The frequency pattern of the human auditory sensation in response to amplitude-modulated (AM) ultrasonic stimulation is observed to be proportional to the frequency spectrum of the square of the modulation functions [Zeng and Beard, J. Acoust. Soc. Am. 93, 2332 (A) (1993)]. In contrast, the frequency pattern of rectifying demodulation is proportional to the frequency spectrum of the absolute values of the modulation functions; and the frequency pattern of coherent demodulation is the spectrum of the modulation functions. The distinct discrepancies in frequency patterns between the auditory sensation in human ultrasonic hearing and the above two physical demodulations indicate that rectifying demodulation and coherent demodulation are irrelevant to human ultrasonic hearing. When the human subject’s cochlear region is stimulated by an AM ultrasonic mode (1+cos 2πFt)cos 2πft, the subject can sense the fundamental modulation frequency F and the weaker second harmonic 2F, where f is the carrier frequency. The amplitude ratio of the intensity threshold for sensing the first harmonic to that for sensing the second harmonic is 0.37 at F=1 kHz, 0.57 at 250 Hz, and 0.68 at 3 kHz. Compared with the same ratio in parametric demodulation, which is 0.9, and in the demodulation caused by the quadratic property, which is 0.25, parametric demodulation is considered to have a joint influence in conjunction with the quadratic property on human AM ultrasonic hearing [Zeng, Ph.D. dissertation, Drexel Univ. (1993)]. [Work partially supported by Electro-Stim Corp.]
Effect of click-repetition rate on acoustic reflex growth
Authors: Rawool Vishakha W.
Published: October 2005

Effects of click-repetition rate on acoustic reflex growth were studied in 11 young female subjects (total 22 ears). The probe tone frequency was 226 Hz and the intensity was 85 dB SPL. Following the determination of ipsilateral acoustic reflex thresholds in response to condensation clicks at repetition rate of 50, 100, 150, 200, 250 and 300/s, reflex amplitudes were measured at levels 5 and 10 dB above the thresholds. For each of the measurements data were obtained across three trials. In 10 of the ears evaluated, data were also obtained at 95 dB peSPL for each of the repetition rate that revealed that acoustic reflex amplitudes increase with increase in repetition rates. A significant effect of repetition rate and sensation level and a significant interaction was apparent for the amplitudes obtained at 5- and 10-dB sensation level (SL). For all the repetition rates 10 dB SL yielded higher amplitudes than those obtained at 5 dB SL except at the 50/s rate where increase in sensation level did not produce any significant increase in amplitudes. Detailed analyses will be presented and the results will be discussed with reference to rate integration in the acoustic reflex pathway. [Work supported by Bloomsburg University Grants for Research and Creative Projects and State System of Higher Education Minority Faculty Development Fund, Pennsylvania.]
Rate integration in click-evoked acoustic reflex thresholds
Authors: Rawool Vishakha W.
Published: October 2005

Effects of click repetition rates on acoustic reflex thresholds were investigated in 11 female subjects (total 22 ears) within the age-range of 20 to 26 years. Acoustic reflexes were elicited in response to ipsilateral condensation clicks of 100-μs duration at repetition rates of 50, 100, 150, 200, 250, and 300/s. The probe tone frequency was 226 Hz and the intensity was 85 dB SPL. Acoustic reflex thresholds were defined at the lowest intensity at which a minimum of 0.02-ml change in admittance was evident on at least two of three trials. The thresholds became significantly better with increase in the repetition rates. The average threshold advantage for the 300/s-click rate over the 50/s rate was 22.5 dB and that of the 100/s rate over the 50/s rate was 12.5 dB. Although such advantage with increase in stimulus repetition rates has been most commonly referred to as temporal integration, a more appropriate term for this phenomenon may be rate integration. Since the firing rates of auditory neurons are known to increase with increase in stimulus intensity, it is conceivable that stimuli presented at higher repetition rates are perceived as being louder. [Work supported by Bloomsburg University Grants for Research and Creative Projects and State System of Higher Education Minority Faculty Development Fund, Pennsylvania.]
Tracking the dynamics of musical instruments based on a high-resolution time-frequency representation
Authors: Pielemeier William J. , Wakefield Gregory H.
Published: October 2005

Attacks and other phenomena that involve rapid amplitude and frequency variations over time present a difficult problem in the study of the dynamics of musical instrument modes. Fourier-series-based methods provide adequate time resolution under the conditions of signal periodicity but performance deteriorates rapidly with gross inharmonicity or large amplitude and frequency transients. Short-time Fourier transform (STFT) methods are most robust to these variations but provide limited resolution in time and frequency. In a previous paper, an alternative time-frequency representation that achieves better resolution than STFT methods, yet remains robust to conditions degrading Fourier series analysis, was presented [Pielemeier etal., J. Acoust. Soc. Am. 92, 2430(A) (1992)]. The present paper develops estimators for modal parameters of musical instruments based on this alternative time-frequency representation. The performance of these estimators is analyzed and compared with that of Fourier series and STFT methods for several musical cases, including the attack transients of trumpet, vibraphone, and flute notes. In general, it is found that the proposed estimators provide a more accurate portrait of the spectral dynamics of the musical signal than is possible using estimators based on the other two representations.
Rayleigh’s horn equation
Authors: Post John T. , Hixson Elmer L.
Published: October 2005

Rayleigh’s work on tapered waveguides is applied to acoustic horns. The acoustic velocity potential is expanded in a perturbation-type solution and the first perturbation is shown to produce the Webster horn equation on-axis, but predicts progressive waves to have curved, or bulging, phase fronts. Applicability of Rayleigh’s first perturbation is shown to be identical to the estimate given by Pierce for applicability of the Webster horn equation and both of these reveal that the Webster equation cannot predict a ‘‘cutoff’’ frequency. When operating at the ‘‘cutoff’’ frequency predicted by Webster, any practical horn is too short to load an acoustic source, so the performance is virtually the same as letting the source radiate into free-space; but the horn does not attenuate the progressive wave below the ‘‘cutoff’’ frequency in the same way that high-order modes are attenuated below their cutoff frequency in an acoustic waveguide. Rayleigh’s second perturbation is presented as ‘‘Rayleigh’s horn equation.’’ The acoustic impedance at the throat of the horn and sound pressure interior to the horn as predicted from Rayleigh’s theory are compared with laboratory measurements.
Underwater sound produced by rainfall: Secondary splashes of aerosols
Authors: Nystuen Jeffrey A. , Medwin Herman
Published: October 2005

Earlier studies have identified three sources of underwater sound production from raindrops: the initial impact, a bubble trapped underwater as the impact crater closes (type I), and a bubble trapped underwater by a turbulent jet associated with the splash canopy formation (type II). For natural rainfall, type I bubbles are associated with small raindrops (0.8–1.1 mm diam), while type II bubbles are associated with large raindrops (diameter greater than 2.2 mm). Predictions for the sound generated by rainfall considering these three sound source mechanisms have been consistently low, suggesting that an additional source mechanism is present. Experimental data will be presented describing a new mechanism of bubble entrapment—namely, bubbles created during the secondary splashes of drop aerosols thrown up during the initial raindrop impact (type III). For the raindrop sizes studied (large raindrops, 3.0–4.7 mm diam), type III bubbles occurred, on average, more than once per impact. These bubbles span sizes, resonance frequencies, and acoustical energy emissions comparable to the type II bubbles. Consideration of type III bubbles improves predictions of the underwater sound generated by rainfall. These predictions are needed to support the inversion of the oceanic ambient sound field to estimated rainfall rate at sea quantitatively. [Work supported by ONR and NRL/TOWS.]
Barotropic currents, vorticity, and tides in the northcentral Pacific in summer 1987 determined from long-range acoustic transmissions
Authors: Dushaw Brian D. , Worcester Peter F. , Cornuelle Bruce D. , Howe Bruce M.
Published: October 2005

Large-scale depth-integrated currents, relative vorticity, and tides were measured in the northcentral Pacific Ocean during summer 1987 using long-range reciprocal acoustic transmissions between transceivers in a triangle approximately 1000 km on a side. Tidal harmonic constants found from the acoustically determined currents agree with those found from current meters and with the tidal models of Schwiderski [E. W. Schwiderski, Mar. Geod. 3, 161–255 (1980)] and Cartwright etal. [D. E. Cartwright etal., NASA Tech. Mem. 104578 (1992)]. Sum travel times were used to calculate the baroclinic tide isotach displacement. A significant part of the derived internal tide is deterministic. Currents are calculated using the topographic Sverdrup balance with the Fleet Numerical Oceanography Center wind field. The measured time derivative of the areal-averaged relative vorticity is insignificant to the Sverdrup balance. Currents and vorticity calculated using the Sverdrup balance are an order of magnitude smaller than the observations. The magnitude and variability of the large-scale currents and vorticity determined from the Semtner–Chervin eddy-resolving model of ocean circulation [A. J. Semtner and R. M. Chervin, J. Geophys. Res. 93, 15 502–15 522 (1988)] are similar to the direct measurements. [Work supported by NSF and ONR.]
Duration modeling with hidden Markov models
Authors: Bosch L. F. M. ten , Wang X. , Pols L. C. W.
Published: October 2005

In hidden Markov modeling (HMM) of speech signals, the statistics of speech characteristics are represented by HMM parameters after the HMM training. This procedure is purely statistical. This study concerns the incorporation of explicit knowledge into the HMM training. Therefore one specific parameter, i.e., segment duration, was selected. In order to study the relation between duration and HMM modeling, three types of duration PDFs (DPDFs) are distinguished: (A) the DPDF defined by the segmented database used (the actual duration histogram); (B) the DPDF defined by the trained Markov model (i.e., by the transition matrix), and (C) the DPDF based on the HMM segmentation. While PDF (A) is based on data and PDF (B) is based on the trained model, PDF (C) combines both features and is based on the available set of observation sequences. First, an explicit relation is formulated between topology of the PLU, the three DPDFs, and the so-called Padé expansion. By using the generatingfunction of the PDPT, it is possible to relate topological properties of PLUs on the one hand and algebraic properties of the DPDF on the other. Second, relations between those PDFs are presented by using two databases containing identical texts, but read aloud with a normal and fast speaking rate. This procedure allows a comparison between variations in the phonetic segment duration and the HMM parameters.
Why users need accurate real-world estimates of hearing protector’s ratings
Authors: Dixon-Ernst C. , Behar A.
Published: October 2005

Accurate values for hearing protectors’ attenuations are needed by occupational health professionals who deal with hearing conservation of employees exposed to noise levels in excess of 85 dBA. The problem becomes yet more important in large corporations with extensive use of those devices. Inaccurate NRR values may be the cause of increases in hearing losses, worker’s compensation claims, and liabilities. Overestimation of the NRR may result in a decrease in the use of engineering noise controls. Each of these areas will be highlighted and explained.
Results of the S12 Working Group 11 interlaboratory study to approximate real-world attenuation of hearing protection devices (HPDs)
Authors: Royster Julia D. , Royster Larry H.
Published: October 2005

Four HPDs, three plugs and one muff, were tested in four labs to identify a protocol that would estimate the real-world attenuation obtained in field studies of workers in hearing conservation programs. Audiometrically experienced subjects who had never worn HPDs regularly used each device, following the manufacturers’ instructions without any supplemental experimenter training (subject-fit condition). Subsequently, after the experimenter demonstrated the use of each device, the subject used each HPD again (informed-user-fit condition). Attenuation was measured in two trials with each HPD in each instruction condition. Practice within a condition yielded no significant improvement in achieved attenuation. Experimenter instruction significantly increased the attenuation subjects obtained with earplugs (but not earmuffs). The subject-fit condition approximated the upper quartile of real-world attenuation, and the range of standard deviations of attenuation across labs was no greater than for the informed-user-fit condition, indicating acceptable reproducibility. Testing earmuffs worn with safety glasses only slightly increased the range of standard deviations.
Hearing protector attenuation from subject-fit methods at the work site and in the laboratory
Authors: Franks John R. , Casali John G.
Published: October 2005

A disparity exists between the advertised and realized attenuation of noise by hearing protective devices. The disparity has been accredited to many factors, including overfitting by experimenters and misuse by workers. This study compared attenuation data for three earplugs and one earmuff obtained from an interlaboratory (IL) study using a subject-fit method with data on the same protectors reported in the literature from work-site (WS) studies where workers fitted the hearing protection and with manufacturer-reported (MR) data on NRR labels. The IL method required subjects who where audiometrically competent, but inexperienced with hearing protectors, to fit hearing protectors relying solely upon guidance from the manufacturers’ written instructions. Results indicated that there were no differences in attenuations between laboratories. Confidence interval testing was performed comparing the IL mean attenuations and variances to WS means and standard deviations and to MR means and standard deviations. Results indicated that the IL data were more consistent with the WS data than with the MR data. In all cases the IL data were significantly less than the MR data. Depending upon protector type, the IL data were equivalent to or greater than the WS data.
Mode-locked sonoluminescence in a sealed system
Authors: Hiller Robert , Barber Bradley P.
Published: October 2005

The means whereby synchronous single-bubble sonoluminescence can be achieved in a sealed system will be discussed. This technique is important for the study of gases and liquids other than air and water and also to maintain a constant partial pressure during an extended experimental run. For temporal stability, sonoluminescence and an oscillator can be mode-locked. Also the sonoluminescencing resonator can be mode-locked to itself. Measurements that make use of these techniques will be presented. [Work supported by the U.S. DOE Division of Advanced Energy Projects.]
Comments on the effect of an acoustic field on the shape oscillations of levitated drops and bubbles
Authors: Asaki Thomas J. , Marston Philip L.
Published: October 2005

Acoustic levitation has been used as a method for measuring the frequency and dissipative properties of shape oscillation modes of drops and bubbles [P. L. Marston and R. E. Apfel, J. Acoust. Soc. Am. 67, 27–37 (1980); T. J. Asaki etal., J. Acoust. Soc. Am. 93, 706–713 (1993)]. One of the problems in the interpretation of such measurements is the effect of the levitating field. Some of the relevant issues for slightly deformed drops or bubbles, where the equilibrium shape is spheroidal and R is the radius of the sphere of the same volume, are examined. The interaction of shape oscillations with the external acoustic flow is approximated for a spheroid at the velocity antinode of a standing wave in the long-wavelength limit (kR→0) with the result that the effective restoring force for the quadrupole mode is increased. The curvature of the effective potential well is increased. The analysis makes use of the known solution for the potential flow past an incompressible spheroid in the kR→0 limit. [Work supported by ONR.]
An overview of fractional-order calculus applied to viscoelasticity
Authors: Bagley Ronald L.
Published: October 2005

Over the past 80 yr, an initially obscure branch of calculus has gained some attention as a compact, mathematically convenient description of linear viscoelasticity. Rieman and Liouville developed the classical definitions of fractional-order integration and differentiation. These definitions are fading-memory, linear operators well-suited for describing relaxation, dispersion, and attenuation effects. Early in this century, several authors suggested adhoc fractional-order differentials to describe viscoelastic effects. Scott Blair first suggested the Rieman and Liouville operators in the early 1940s. Several investigators have subsequently echoed Scott Blair’s suggestion. More recently, the fractional-order calculus viscoelasticity formulation has been expanded to include dynamics and finite-element formulations. Most recently, the formulation has led to the development of the thermorheologically complex model, a generalization of the thermorheologically simple material model, and the model has been related to molecular bond energy decay and fractals. Other recently developed engineering applications of fractional calculus include corrosion, aeroelasticity, and feedback control.
A spectral method for calculation of ocean acoustic normal modes using Chebyshev polynomials
Authors: Dzieciuch Matthew A.
Published: October 2005

A new method employing Chebyshev polynomials to calculate the underwater acoustic normal mode equation was developed. The method is a spectral approach using Chebyshev polynomials as basis functions. This expansion has the advantage of being a particularly efficient and accurate representation of the normal modes (especially of the lower order) since they give an exceedingly good representation of narrow boundary layers such as the sound-speed profile that can undergo rapid changes near the surface. This representation reduces the size of the eigenvalue problem to be solved. Since the CPU time scales with N3, where N is the size of the matrix, any size reduction is an advantage computationally. This approach has a significant speed advantage over finite difference methods without sacrificing accuracy. A Chebyshev representation is usually remarkably close to the minimax polynomial that minimizes the maximum error implying high accuracy. Chebyshev polynomials are also useful for the calculation of quantities involving the integral of the mode function, such as modal group velocity, loss, and coupling coefficient matrices in non-adiabatic propagation environments. These quantities can be calculated easily and accurately given their spectral representations without introducing any further numerical error.
A normal-mode theory of shallow-water reverberation
Authors: Zhang Renhe , Jin Guoliang , Guan Dinghua , Li Wenhua , Qiu Xinfang
Published: October 2005

Shallow-water reverberation is mainly caused by bottom scattering, and is much more complicated than the deep-water one. Ray theory can be used for calculating short-range reverberation simply by ignoring the water inhomogeneity, but is not suitable for long-range reverberation due to effects of refraction and multipath transmission. Assuming that the scattering sources are homogeneously distributed on the bottom and regarded as the secondary sound sources with certain directivity, by using the WKBZ approximation a normal-mode theory suitable for long-range reverberation is developed. Because the effects of the complex eigenvalues on the mode incident field have been considered, the theory is better than the former ones. The given expressions of reverberation intensity have explicit physical meaning and concise form so that they are easily used for numerical calculation and analytical discussion. Both theory and experiment show that the reverberation in inhomogeneous shallow water has obvious depth dependence and there exists the relationship: IR(r,z1,z2)=[IR(r,z1,z1)×IR(r,z2,z2)]1/2. Some experimental results are given that are consistent with theory.
Scattering from frontal structures, internal tides, and internal waves during the 1992 Barents Sea polar front experiment
Authors: Chiu Ching-Sang , Miller James H. , Jin Guoliang , Ray Douglas , Lynch James
Published: October 2005

In August 1992, a coastal ocean tomography experiment was conducted in the Barents Sea over the steep northwestern slope of the Bear Island Trough, about 100 km east of Bear Island. The oceanographic objective of the experiment was to study the dynamics of the polar front and its vicinity using both acoustic tomography and traditional hydrographic techniques. The acoustic objective was to study the effects of the front and other coastal oceanography on the acoustic propagation. These objectives are strongly coupled, in that to effectively perform an inverse for the ocean features, one must first obtain a good understanding of the ‘‘forward problem.’’ In this paper, the effect of the strong frontal interface is examined, including its corrugations (‘‘interleaving’’ features), internal tides, and internal waves on the observed acoustic propagation. Effects on both the modal and ray propagation pictures will be examined, using both theoretical predictions and experimental data.
Matched-field 3-D tomographic inversion for geoacoustic parameters
Authors: Tolstoy A.
Published: October 2005

Matched-field processing has recently been applied to the determination of a wide variety of environmental parameters. However, nearly all efforts have been directed toward determining those parameters along a 2-D swath through the environment. The approach developed for the tomographic 3-D calculation of deep ocean sound-speed profiles [Tolstoy etal., J. Acoust. Soc. Am. 89, 1119–1127 (1991); Tolstoy, J. Acoust. Soc. Am. 91, 781–787 (1992)] has now been adapted for the determination of bottom properties, i.e., sediment thicknesses, sound speeds, and densities. The inversion technique will be discussed and calculations in shallow water environments, where bottom properties are of paramount importance, will be presented.
A higher-order stochastic model for surface backscatter in high sea states
Authors: Gilbert Kenneth E. , Ameling Lucy J.
Published: October 2005

A stochastic bubble-layer scattering model based on first-order perturbation theory (plane-wave Born approximation) has recently been developed [K. E. Gilbert, submitted to J. Acoust. Soc. Am. (1993)]. In the first-order model, the scattering is treated as a perturbation on the plane-wave solution for the bubble-free water and is written in terms of a ‘‘geometric factor’’ times the horizontal wave-number spectrum of the sound-speed fluctuations in the bubble layer. For low sea states and higher grazing angles, this approach is adequate. For high sea states and low grazing angles, first-order perturbation theory is less accurate and one needs to account for the average bubble density and compute backscatter due to fluctuations about the average. In this paper results are compared for scattering computed with the ordinary plane-wave Born approximation to that computed with the ‘‘distorted-wave’’ Born approximation (DWBA). It is shown that for high sea states and low grazing angles, distorted waves significantly enhance the backscatter at low frequencies and consequently give better agreement with experiment. The effect can be understood in terms of near-surface upward refraction that creates greater insonification and larger grazing angles near the surface than that obtained with plane waves. Finally, the effect of near-surface upward refraction on rough surface scattering is briefly discussed.
Experimental observations of phase dislocations in shallow water waveguides
Authors: Shmelerv A. Yu. , Migulin A. A. , Lynch James F.
Published: October 2005

Previous work by Petnikov [Akust. Zh. 37, 1212–1215 (1991)] and Shmelerv etal. [J. Acoust. Soc. Am. 92, 1003–1007 (1992)] has shown fast phase fluctuations of up to 180° in low-frequency continuous-wave (cw) signals measured during the Coastal Barents Sea Acoustic Test Experiment. These fast fluctuations can be explained as phase dislocations passing through the receiving array [Kravtsov etal., Sov. Phys. Acoust. 35, 156–159 (1989)]. Recent investigations of linearly modulated broadband acoustic signal propagation in the same region have also shown some features associated with phase dislocations passing by. It was found that the frequency at which a dislocation occurs changes slightly because of ocean variability. This frequency can be considered as a parameter of the acoustic field variability. The results of experimental observations of phase dislocations in several shallow water cw and broadband experiments are summarized. Discussion of these experiments will include suggestions on the use of the dislocation approach in tomographic schemes.
Bottom backscattering strengths derived from shallow-water reverberation measurements
Authors: Ellis Dale D. , Preston John R.
Published: October 2005

A normal-mode model for calculating surface and bottom reverberation in shallow water has been developed, and found to give good agreement with single-hydrophone data for a fairly flat-bottomed area [D. D. Ellis, SACLANTCEN Report SR-196 (September 1992)]. The model has been extended to include beam patterns and has been compared with broadband data received on a horizontal line array. The model-data agreement is again generally quite good. When the model-data differences as a function of beam angle and time are overlaid on a map of the area, the differences are seen to be primarily due to changes in the bottom bathymetry. This can be used to extract a measure of the bottom backscattering strength versus location.
Accuracy of dynamic modulus measurements made with the dynamic mechanical thermal analyzer
Authors: Deigan R. J. , Dlubac J. J.
Published: October 2005

The accurate determination of the complex moduli of viscoelastic materials is of great importance for the efficient design of many noise control devices. It is often the case that a design, in conjunction with its acoustic performance requirements, leads to a narrow band of acceptable dynamic modulus for the viscoelastic material. In such cases knowledge of the accuracy and reliability of the measurement apparatus is essential. Dynamic complex shear modulus is measured at Carderock Division Naval Surface Warfare Center (CDNSWC) with the Dynamic Mechanical Thermal Analyzer (DMTA), manufactured by Polymer Laboratories. An attempt to quantify the absolute accuracy of the DMTA measurement has been made through the consideration of errors including the accuracy of the beam solution used to infer the complex modulus, compliance of the sample mounts, measurement noise, temperature control, thermal stress, Poisson effects, and the implementation of time-temperature superposition. With these considerations, an ad hoc error analysis is implemented to quantify absolute error bounds expected for DMTA measurements of a hypothetical material. These results are of direct interest to the ASA Committee on Standards S2WG79, ‘‘Characterization of the Dynamic Properties of Viscoelastic Polymers,’’ which has initiated round-robin testing among committee participants. CDNSWC results from the DMTA tests of three round-robin materials will be presented.
Phonatory instability in ALS dysarthria: A case study
Authors: Buder Eugene H. , Strand Edythe A.
Published: October 2005

A subgroup of patients with dysarthria resulting from amyotrophic lateral sclerosis (ALS) presents with voice problems characterized primarily by cycle-to-cycle and long-term phonatory instabilities. This paper reports acoustic analyses of the phonation of a 63-yr-old female 9 months post diagnosis of ALS. Perceptual characteristics of voice included inconsistent harshness and cyclic variations in both pitch and loudness. Spectral analysis of fundamental frequency (f0) and intensity contours revealed periodic instabilities at multiple temporal domains, including 0.4- and 0.8- Hz cycles in both f0 and intensity (‘‘wow’’), 2-Hz cycles in f0 (‘‘tremor’’), and 11-Hz cycles in intensity (‘‘flutter’’). Phase relations were noted among these cycles and with other acoustic analysis parameters such as perturbation and spectral energy distribution, indicating that occurrence of short-term and cycle-to-cycle instabilities was modulated by the longer term cycles. The results are discussed with relation to video stroboscopic examinations of this patient, and also in comparison with phonatory characteristics of other patients in this subgroup (females with ALS related voice problems). [Work supported by NIH.]
Low-frequency time-dependent scattering from evolving bubble plumes: Theory and numerical results
Authors: Gragg Robert F. , Wurmser Daniel
Published: October 2005

This work advances the capability for modeling the scattering from near-surface bubble plumes beyond the static approximation. Plumes were modeled as evolving structures having finite lifetimes (∼10 s) with distinct growth and decay stages. The scattering response of such a plume was formulated in terms of the theory of linear time-varying (LTV) filters. Complex scattering amplitudes within the frequency band of interest (50–500 Hz) were computed using either partial wave analysis [for (hemi-) spherical shapes] or boundary integral equation (BIE) methods (for more general shapes). For cw inputs, groups of pseudo-Doppler side peaks were observed in the scattered spectra as a result of the time evolution of the target’s internal resonances. Several broadband source waveforms were considered to assess their effectiveness as experimental probes for observing transient near-surface plumes in the field. [Work supported by ONR, Code 4530.]
Multiple scattering effects in scattering from a target in shallow water
Authors: Sarkissian Angie
Published: October 2005

Scattering from a target in a bounded medium involves both propagation effects and target scattering effects as well as the coupling of the two. Previously, in order to simply the problem, the coupling of the two effects had been neglected by ignoring the contribution of multiple scattering between target and shallow water boundaries. This has been highly desirable because it eliminates the need to evaluate the shallow water Green’s function over short ranges. Scattering computations are made to show the importance of including this coupling effect even at relatively low frequencies. It is shown that if the target is closer to the surface than the bottom, then the main contribution of the multiple scattering is due to the interaction of the target with the top surface and this effect may easily be included when the method of superposition is applied.
A cross-correlation model of common-period grouping
Authors: Ellis Daniel P. W.
Published: October 2005

When extracting and identifying vowels from noisy backgrounds, the human auditory system must identify which frequency regions ‘‘belong’’ to the vowel (as formants), and which are extraneous. This is probably based, at least in part, on the common pitch-period amplitude-modulation of all these regions. Previous computer models of this process have used autocorrelation to identify this cue within each channel of a bandpass array [R. Meddis and M. J. Hewitt, J. Acoust. Soc. Am. 91, 233–245 (1992)]. Autocorrelation, however, is less effective for signals exhibiting rapid frequency modulation or jitter, even though these are strong cues to fusion. A model is proposed that detects comodulation synchrony between frequency bands through a simplified nonlinear approximation to the cross-correlation function. By grouping bands that show a steady modulation skew, pitch-period fluctuation can be used to reinforce grouping rather than weaken it. The physiological plausibility of such a process is also argued.