bluuebunny/crossref_metadata_2025 huggingface dataset:
The effect of intensive voice therapy on speech and voice deficits in atypical Parkinson’s disease
Authors: Countryman Stefanie M. , Ramig Lorraine O.
Published: October 2005

Acoustic data were collected twice pre-treatment, once post-treatment, and 6 months post-treatment on three atypical Parkinson’s disease patients following intensive voice therapy. Using a custom-built software program, the following variables were measured: maximum duration of sustained vowel phonation and sound pressure level from sustained vowel phonation, a standard passage, and spontaneous speech. Using the C-Speech application [Milenkovic, J. Speech Hear. Res. 30, 529–538 (1987)], fundamental frequency variability was measured from a standard passage and spontaneous speech. Single-word intelligibility was calculated using naive listeners’ perceptions. The patients achieved statistically significant improvement on all variables post-treatment but did not maintain improvement as a group during reading and spontaneous speech by the 6-month data collection session. These results suggest the effectiveness of intensive voice treatment in atypical Parkinson’s disease as well as provide insight into the underlying pathophysiology of their speech and voice deficits. Due to the limited length of time post-treatment levels were maintained, a longer period of therapy as well as follow-up therapy sessions are recommended for this population. [Work supported by NIH Grant No. RO1 DC01150-03 and NIDCD Grant No. DC00976.]
Quantitative analyses of thyroarytenoid activity in spasmodic dysphonia
Authors: Watson Ben C. , Roark Rick , Schaefer Steven
Published: October 2005

Perceptual ratings of vocal abnormality in spasmodic dysphonia (SD) are confounded by high variability in the severity, quality (strain-strangle versus aspirate), and task sensitivity of symptoms. Perceptual ratings are also relatively distant from the physiologic source of vocal disruption. Investigations at the neuromuscular level are closer to the source of disruption and may be informative. Thyroarytenoid myoelectric activity was recorded while SD and normal control subjects produced multiple tokens of sustained vowel, word repetition, and sentence tasks. Quantitative amplitude measures were submitted to several principal components analyses to develop models of neuromotor abnormality in SD. Analyses yielded quantitative indices of the magnitude and task-sensitivity of thyroarytenoid activity. A between-group model that included one measure across the three tasks achieved 100% discrimination of normal control and SD subjects on one component. The within-group model failed to separate perceptually different subgroups of SD subjects along either component considered separately. Models challenge the validity of the traditional clinical distinction between abductor and adductor SD and the validity of perceptual ratings of vocal spasms in spasmodic dysphonia. [Work supported by NIH Grant No. DC-00410.]
A microcomputer-based clinical voice aerodynamic measurement system
Authors: Poburka Bruce J. , Milenkovic Paul H. , Bless Diane M.
Published: October 2005

The authors’ clinical experience with dedicated instruments for voice aerodynamic measurements prompts them to implement these measurements on a microcomputer system. A microcomputer system can be lower in cost, it facilitates archival storage of data, it offers the flexibility of changing what is measured and it offers automated post processing. A system measuring flow, intensity, intraoral pressure, and pitch is implemented on a PC compatible computer, using an Intel 486 microprocessor, running the CSpeech waveform acquisition and analysis software. The salient enhancements to CSPeech used to implement this system are described. The record command was modified to provide visual feedback of voice aerodynamic efficiency, and a pause/resume feature simplifies clinical voice recording procedures. Filter scripts were developed to provide a flexible way to specify analysis procedures and formats for archival storage and retrieval. The filter script is based on the object-oriented concept of specifying both the data and a method for analyzing or archiving the data in the desired form.
Measurement accuracy of the Glottal Enterprises pneumotach system
Authors: Scherer Ronald C. , Dromey Christopher , Guo Chwen-Geng
Published: October 2005

An important instrument for measuring airflows in speech is the pneumotach system provided by Glottal Enterprises. Inverse filtering the measured airflow allows the estimation of glottal volume velocity. The face mask (MSIF-2) has numerous wire-meshed holes placed approximately in the plane of the lips. Airflow from the mouth during speech may come out in a directed stream, creating nonuniform flow through the mask and measured pressures (Micro Switch) that do not reflect the correct flow. Results for cylindrical tubes representing mouth openings indicate that the angle of the flow makes a difference: e.g., for a flow of about 700 cc/s projecting upward versus downward at 45-deg angles, the difference in estimated flow is 100–250 cc/s for a small tube opening (0.2 sq cm). The difference is only about 10 cc/s for a medium size mouth opening of 2.0 sq cm. Also, results indicate that equipment drift is a minor concern, flow estimates are negligibly different for the expected range of face protrusions into the mask for the medium mouth opening, and the effects of temperature change were negligible. Results will be discussed relative to the accuracy of flow measures for particular speech and voice sounds.
A two-tap pitch predictor for measuring voice aperiodicity noise at high SNR
Authors: Leddy Mark , Milenkovic Paul H. , Bless Diane M.
Published: October 2005

The measurement of aperiodicity noise in the human voice is complicated by the multiple source of this noise. While turbulence noise at the glottis is hypothesized to contribute to aperiodicity noise, it is known that waveform jitter, the cycle-to-cycle fluctuation in pitch period, contributes significantly to the measured aperiodicity noise. In seeking to reduce the influence of jitter on measured noise, it has been observed that a cross-correlation pitch tracker based on a sliding analysis window exhibits the greatest change in measured pitch period when the window crosses a glottal-closure epoch. It was hypothesized that the accuracy of a pitch-predictor based measurement of the noise could be improved if one knew the correct alignment of the analysis window relative to the glottal epoch. In the absence of this knowledge, for each update of a short-term analysis, two alignments of the window were used and that alignment with the least-square pitch predictor error was selected. This leads to a computationally efficient algorithm that does not require explicit determination of glottal epochs. Preliminary trials on subjects with high SNRs indicate a reduced influence of jitter on the observed SNRs.
Auditory apparent motion in the horizontal and median planes
Authors: Strybel Thomas Z.
Published: October 2005

The range of stimulus durations and interstimulus onset intervals (ISOIs) that produced the illusion of auditory apparent motion (AAM) were measured when two sound sources were separated in either the horizontal or median planes. Three speaker arrangements were tested, 350° and 10° azimuth at 0° elevation, 0° and 180° azimuth at 0° elevation, and 0° and 20° elevation at 0° azimuth. Subjects were instructed to categorize their perception of the stimulus sequence into one of five categories that were based on the number of sources heard and whether or not motion was perceived. Subjects also indicated the relative location of the leading stimulus. For each speaker arrangement, stimulus durations of 10, 25, and 50 ms and ISOIs between 2 and 70 ms were tested. The plane in which the sources were located did not affect the timing conditions that produced the illusion of motion. AAM was heard for stimulus durations of 25 and 50 ms at ISOI values that were roughly equal to stimulus duration for all of the speaker arrangements tested. However, judgments of the location of the leading source were affected by the arrangement of the speakers. Performance on this task was best when the sources were separated in the horizontal plane.
Green’s functions for wave propagation in range-dependent inhomogeneous media—Some exact analytic solutions
Authors: Li Y. L.
Published: October 2005

Three exact analytic solutions of the Helmholtz equation are obtained in closed form for the case of a point source in range-dependent inhomogeneous media. The solutions are obtained by starting with a onefold integral representation for the solution that is derived from the path integral. For a point source in such media above either a soft or hard ground, the exact analytic solutions are also derived. These solutions are particularly useful for testing the validity of approximate or numerical solutions for cases with a range-dependent background medium. They also facilitate construction of more general solutions for problems with scattering in a range-dependent background medium, through the use of integral equation techniques.
Computational and experimental investigation of time-shift estimation for compensation of wave-front distortion in ultrasonic applications using scattered signals
Authors: Kanda Ryoichi , Liu Dong-Lai , Waag Robert C.
Published: October 2005

Time-shift compensation of wave-front distortion that degrades images in medical ultrasound has been studied using computations and measurements. In the computations, wave-front distortion was assumed to arise from a phase screen placed at various distances from the receiving aperture. Intensity patterns were determined from uncompensated data and from data compensated with time-shift estimates made in the aperture. In the experiments, waveforms scattered by a wire target and randomly distributed particles were collected for a water path and for a tissue path. Images were reconstructed from uncompensated data, from data compensated with time-shift estimates made in the receiving aperture, and from data compensated with time-shift estimates made after a backpropagation step in which a waveform similarity factor was maximized. The results show the limitations of time-shift estimation in the aperture for compensation of wave-front distortion produced by a phase screen that is not close to the receiving aperture. The results also show that the addition of a backpropagation step before time-shift compensation can improve the characteristics of the focus.
Acoustic band structure in liquids and gases—fcc pattern with spherical balloons
Authors: Kushwaha M. S. , Halevi P.
Published: October 2005

The first extensive band structure calculations in periodic structures made up of liquids and gases are reported. The specific system studied in the present investigation is spherical air (water) balloons in a periodic pattern in water (air)—the fcc arrangement. Since only longitudinal waves can propagate, the general wave equation is greatly simplified. The pertinent parameters are the densities and the longitudinal-sound velocities. Depending upon the filling fraction a number of band gap(s) extending over the whole first Brillouin zone are found. Within these band gaps vibrations and sound propagation are prohibited. A complete acoustic gap or zero density of states should have important consequences for the realization of noiseless environment and for the localization of longitudinal sound waves. The precise dependence of the band gaps on the filling fraction is also investigated.
The study of the influence of boundary layer effect upon the standing wave in an open resonator
Authors: Benson Yulia J.
Published: October 2005

A simplest model approach to the problem of the study of nonlinear processes in an open resonator is proposed here. It is based on the consideration of the only act of propagation—reflection of the wave in an open-ended tube. In other words, one can study the incoming wave distortion during wave propagation forward to the closed end (piston) and backward. According to the experimental data the process of oscillation in some cases is mostly defined by these distortions. For example, the experiment [B. Sturtevant, J. Fluid Mech. 63, pt. 1, 97–120 (1974)] predicts that a shock wave should be formed during the propagation considered. The numerical analysis of the standard Burgers’ equation plus the term that was derived by Blackstock [D. T. Blackstock, J. Acoust. Soc. Am. 77, 2050–2053 (1985)] in order to describe an influence of the boundary layer at the walls on plane traveling waves allows one to conclude that an account of this effect permits one to obtain a good agreement with the results predicted by Sturtevant’s experiment. Moreover such a statement can be regarded as an inverse problem, so that it is possible to restore the boundary condition using the experimental data.
Locating two uncorrelated sound sources with two vector sound-intensity probes
Authors: Hickling Robert , Morgan Alexander P.
Published: October 2005

The use of vector sound-intensity probes for locating sound sources is a relatively undeveloped area. In a prior presentation [Hickling etal., J. Acoust. Soc. Am. 93, 2357 (A) (1993)] it was shown experimentally that the direction of a single source in water could be detected within ±2 deg using a probe with four pressure transducers. It was also known that the effect of noise interference from another source could be removed by spectral subtraction. In the present presentation, numerical continuation methods are used to solve a set of nonlinear equations to determine the coordinates and strength of two uncorrelated sound sources from measurements with two vector probes.
The impulse response of rough two-dimensional surfaces
Authors: Keiffer Richard S. , Novarini J. C.
Published: October 2005

Previously, a model for the impulse response of rough two-dimensional (2-D) surfaces, based on an extension of the wedge assemblage method, has been described (R. S. Keiffer etal., Proceedings of the Second IMACS Symposium on Computational Acoustics, Vol. 1, p. 67), In the time that has elapsed since this fully 3-D scattering model’s original development, the validity of the WA model, which was questionable for smooth, unwedge-like surfaces has clearly been established for 2-D surfaces [R. S. Keiffer, J. Acoust. Soc. Am. (to be published)]. More recently, the extension of the WA method that allows for the application of the technique to fully 2-D surfaces has been rigorously tested in a numerical study involving scattering from thin disks (R. S. Keiffer etal., submitted to J. Acoust. Soc. Am.). With the validity of the WA method less in question, and with the increasing availability of benchmark quality solutions (albeit in the frequency domain) for the fully 3-D problem, it seems appropriate at this time to review the 3-D wedge assemblage scattering program (WASP 3D) and to begin a benchmarking exercise. [This work has been supported by ONR.]
The fine scale oceanography of the Arctic Ocean: Doppler acoustic studies
Authors: Pinkel Robert , Merrifield Mark
Published: October 2005

Focus is on fine-scale studies of the upper Arctic Ocean using a variety of Doppler sonars constructed at the Marine Physical Laboratory. From two Spring experiments in the Beaufort Sea (AIWEX, 1985; LEADEX, 1992), considerable insight has been gained into the climatology of the internal wave field. The most energetic constituents of the wave field, near inertial currents, have very different amplitudes and scales than at lower latitudes. The generation of these waves below the ice and lead-covered surface is considered as a possible factor for their unique characteristics in the Arctic. In order to map the current field below an Arctic lead, a sector-scan Doppler sonar has been developed. Using beamforming techniques, the sonar resolves acoustic backscatter and current speed along 28 contiguous beams with an angular resolution of 1.5°. The sonar was deployed at two leads during the LEADEX experiment. Observations were obtained from a 45° vertical fan directed normal to the lead axis. In these leads, convection associated with atmospheric cooling did not modify strongly the background velocity field. However, a clear increase in acoustic backscatter was detected just below the base of the mixed layer, possibly associated with convective processes.
Broadband geoacoustic inversion in shallow Arctic water
Authors: Wolf John W.
Published: October 2005

A broadband technique used successfully to localize acoustic sources and determine water depth and array position at a deep Pacific Ocean site [P. C. Mignerey, Oceans ’90 Proc., 121–124] is used to determine geoacoustic parameters at a shallow water site in the Arctic. The technique minimizes differences between calculated impulse response times and pulse arrival times measured on a vertical array. Initially the method is used to localize the source (SUS) and determine bottom depth and array orientation. The method is then applied to pulse arrivals that penetrate the upper sedimentary layers of the shallow bottom. The inversion provides compressional speed profiles and sediment layer thicknesses of the bottom near the array site. Differences between calculated arrival times and data show a significant decrease, i.e., improvement, when using the geoacoustic profile as determined by the inversion technique. Broadband matched-field processing is used to demonstrate inversion effects on processor performance. The results demonstrate the broadband method to be useful for geoacoustic surveys of shallow water environments.
A hotel perspective on meeting room sound
Authors: Ash Irv
Published: October 2005

Meeting planners base their decision to stay at a particular hotel, or use a hotel meeting space, on expectations influenced through a travel agent, an advertisement, word of mouth, past experience, or any number of other ways. Regardless of motivation, service and comfort are the primary factors in the decision making. Comfort, like service, is a combination of techniques and ingredients. Discomfort is due to a distortion of these techniques and ingredients. In the hospitality industry, discomfort can often be avoided by getting to know the meeting planner, the needs of the group, and their expectations. Because hotels are generally noisy places, in order to ensure guest comfort it is advantageous when refurbishing or building a hotel to work with a designer who is expert in acoustical treatment.
Acoustical design of meeting rooms—A moving target
Authors: Wetherill Ewart A.
Published: October 2005

The term meetingroom encompasses a broad range of facilities, from small, single-purpose conference rooms to very large convention spaces that are capable of being subdivided and of accommodating simultaneous exhibits, banquets, athletics, and performing arts events. Common to all of these uses are the requirements for control of intruding noise and reverberation, optimizing speech intelligibility and overall sound quality, and use of sophisticated audio visual and teleconference systems. These requirements present opportunities for innovative designs in which acoustical flexibility can optimize usability for many diverse functions. Difficulties to be resolved include constraints imposed by competing design requirements, conditions recently mandated by Americans with Disabilities Act (ADA) statutes, severely restricted budgets, and a general lack of understanding of acoustics issues on the part of clients and builders. This paper reviews typical design issues, with examples from recent projects and with particular emphasis on the importance of familiarity with the many acoustical pitfalls inherent in the design and construction process.
Audio-visual equipment noise in the meeting room—An uninvited participant
Authors: Alexander Martin
Published: October 2005

Even meeting spaces that have been designed to have excellent acoustics and low background noise can exhibit noise problems when audio-visual equipment is introduced into the room. Several common A-V equipment types were evaluated with the goal of assessing sound power, tonal content, and directivity. Results of the measurements, and predicted NC and speech interference levels are presented. Concepts for design of quiet equipment are discussed.
An assessment of automotive sound quality
Authors: Hodgdon Kathleen K.
Published: October 2005

The intent of this research was to define and validate a statistically sound subjective presentation procedure while gathering additional information on individual preferences for sound quality in the passenger compartment of a six-cylinder car. Samples of noise spectra in the passenger compartments of four six-cylinder vehicles were recorded in both steady and accelerating modes of operation. These noise spectra were then presented in a multiple-comparison listening task to 40 individuals for subjective evaluation and ranking from most to least preferred. A nonparametric statistical analysis of the data was completed utilizing the Friedman two-way analysis of variance by ranks. The data were analyzed overall as a function of vehicle and as a function of demographic subgroups of the subjects. A retest of 20 subjects was administered approximately 1 month after initial testing to assess the reliability of the procedure. [This research was sponsored by Advanced Powertrain Engineering, Ford Motor Company.]
Thermodynamic performance of a high-power thermoacoustic refrigerator
Authors: Perkins David K. , Gaitan D. Felipe , Russell Richard , Gopinath Ashok , Morris L. Todd , Mayfield James A. , Garrett Steven L.
Published: October 2005

The cooling capacity of a high-power thermoacoustic refrigerator that uses resonant high-amplitude sound in inert gases to pump heat will be measured and discussed. The thermoacoustic engine under study utilizes two thermoacoustic drivers each capable of delivering 60 W of acoustic power at 325 Hz. The engine is designed to deliver 205 W (700 BTU/h) of useful cooling capacity at 4 °C (refrigerator mode) and 117 W (400 BTU/h) at −22 °C (freeze mode). The engine includes two ‘‘stacks’’ with heat exchangers at each end. Using differential thermopiles, the temperature difference across the inlet and outlet of each of the four heat exchangers is combined with the fluid mass flow rate to quantify heat flow. The determination of the acoustic power delivered to the resonator, combined with the heat flows, forms a complete set of thermodynamic measurements which permits accurate determination of the thermoacoustic coefficient-of-performance. These measurements allow optimization of fluid flow rates. [Work supported by NASA—Life Science Division, the NPS Direct Funded Research Program and the Rolex Award for Enterprise.]
Effective heat transfer between a thermoacoustic heat exchanger and stack
Authors: Hofler Thomas J.
Published: October 2005

Typically, hot and cold copper fin heat exchangers couple heat into and out of the stack. Effective heat transfer means that large amounts of heat are carried across the stack interface with a small temperature difference. Effective heat transfer is also efficient if thermoviscous losses in the heat exchanger are minimized. This is particularly difficult to achieve in engines having high-power density and large gas displacement amplitudes. A simple model for heat exchanger effectiveness and its relationship to fin length and spacing is discussed. Heat exchanger fins that are shorter than the peak gas particle displacement can be effective if the fin spacing is sufficiently small.
Noninvasive phonation threshold pressure estimates: Some methodological considerations
Authors: Fisher Kimberly
Published: October 2005

Phonation threshold pressure (PTP) is the minimum subglottal pressure required to initiate vocal fold oscillation. This pressure is important both theoretically and clinically because of its relationship to tissue viscosity, time varying glottal flow, and vocal tract acoustics. The effects of several different measurement methods on estimated PTP were studied in normal subjects. Oral pressures during quietly voiced consonant–vowel–consonant syllable strings were used to estimate PTP. Factors expected to impact PTP estimates included: (1) low nasal flows associated with soft, relaxed phonation, and (2) vowel context, due to possible reactive loading. A significant percentage of normal subjects evidenced low, inconsistent nasal airflow during /p/ occlusion near threshold (as indicated by nasal pneumotachography). Nasal flow was not associated with supra-threshold production for these same subjects. In spite of similar instruction and pre-recording practice, subjects varied in the strategies they used to accomplish phonation at soft levels near their threshold pressure. Strategies potentially involving slight adjustment in glottal adduction were observed and would be predicted to alter PTP. These methodological challenges will be discussed relative to the variability observed in PTP estimates, and the potential impact on validity and reliability of noninvasive oral pressure measurement.
The effect of gas density on glottal vibration and exit jet particle velocity
Authors: Bielamowicz Steven , Berke Gerald S. , Kreiman Jody , Gerratt Bruce R. , Green David C. , McGowan Richard S.
Published: October 2005

Although theoretical studies include a term for gas density in their mathematical descriptions of glottal aerodynamics, no studies have measured the effect of gas density on glottal vibration and particle velocity. This study used a constant temperature anemometer in the invivo canine model of phonation to evaluate the effect of gas density on subglottic pressure, particle velocity, and glottal vibration by comparing phonation with air and helium. With gas flow and laryngeal nerve stimulation held constant, peak subglottic pressure was significantly greater during helium phonation (70 cm Hg) than during air phonation (62 cm Hg). In addition, peak particle velocity during helium phonation (45 m/s) was significantly greater than phonation with air (34 m/s). However, the increase in particle velocity with helium compared to air was less than predicted by the Bernoulli relationship. This loss in velocity likely represents turbulent and frictional forces at the glottal outlet.
Inferring articulator positions from acoustics: An electromagnetic midsagittal articulometer experiment
Authors: Hogden John , Lofquist Anders , Gracco Vincent , Oshima Kiyoshi , Rubin Philip , Saltzman Elliot
Published: October 2005

To examine the mapping from acoustics to articulation, simultaneous articulatory and acoustic measurements were made of 90 vowel-to-vowel transitions produced by a Swedish speaker. Articulator positions were measured using an electromagnetic midsagittal articulometer that tracked seven receiver coils placed on the lips, jaw, and tongue. The vocal tract transfer function associated with each articulator position was estimated using cepstral analysis on short windows (25.6 ms) of the acoustic signal. The transfer functions were then vector quantized, giving each articulator configuration a corresponding vector quantization code. Given an acoustic signal and its corresponding vector quantization code (code 1 for example), an estimate of the position of any coil during the production of a speech signal can be made by averaging all the positions the coil assumed during the production of sounds labeled with vector quantization code 1. This produces a codebook that allows articulator positions to be estimated from acoustic signals. On a data set not used for training, correlations between estimated and actual receiver coil positions vary strongly with the place of attachment, but correlations above 0.9 are common for coils on the tongue. [Work supported by NIH.]
The 3-D-tongue FEM model revised
Authors: Wilhelms-Tricarico Reiner , Wu Chao-Min
Published: October 2005

As a first application of a newly developed object-oriented finite element code that is specialized for the modeling of biological tissues we have been reimplementing the geometry of the tongue model by S. Kirtani etal. (‘‘A computational model of the tongue,’’ Ann. Bul. Res. Inst. of Logopedics and Phoniatrics, Univ. Tokyo, Vol. 10, pp. 243–251). The new implementation uses large strain and dynamic modeling of the tissue, includes the effects of inertia and observes precisely a weak formulation of the incompressibility constraint of the tissue. The muscle activation input for the current model is made similar to the original computation. However, a different, more realistic nonlinear muscle model is used, in which the active stress depends on the instantaneous strain and strain rate in the direction of the muscle fibers. The implementation methods and computational results will be presented. [Work supported by the Whitaker Foundation and by ATR-International.]
Backscatter from gas bubbles in muddy sediments
Authors: Boyle Frank A. , Chotiros Nicholas P.
Published: October 2005

Recent experimental evidence suggests that trapped gas bubbles may be dominant in backscatter from sandy sediments. A model based on scattering from a spatial distribution of resonant bubbles was previously used to predict shallow grazing angle backscatter from sandy sediments [F. A. Boyle and N. P. Chotiros, J. Acoust. Soc. Am. 93, 2397 (1993)]. A similar model is developed for predicting backscatter from muddy sites. The sediment gas fraction is treated as a free parameter in fitting model predictions to measured backscattering strengths. Model predictions are compared with experiment. [Work supported by NRL/SSC.]
Fracture of sea ice
Authors: Dyer Ira
Published: October 2005

The major cause of ambient noise in the Arctic Ocean is radiation from the fracture of sea ice in response to environmental forcing. Extant noise data on fracture in pack ice in the central Arctic and in free-drifting ice at its margins, including measures such as spectral density, temporal evolution, and individual ice fracture transients and their statistics are reviewed. Physical mechanisms responsible for ice fracture are of fundamental interest, and therefore the fracture mechanics of sea ice, which leads to a picture of ice failure not unlike that of failure in the Earth’s crust via earthquakes, is also discussed. As in earthquakes, ice fracturing is a process of many small fault plane motions which can result in a major ice crack. Prospects for use of noise measurements to understand ice processes immediately come to mind, as well as their use intrinsically to describe acoustic properties of the Arctic Ocean.
Recent approaches to the acoustic-seismic study of ice mechanics
Authors: Farmer David M. , Xie Yunbo
Published: October 2005

Acoustic and seismic emissions provide useful information on the mechanical properties of sea ice and its response to stress. Two recent field studies carried out under the ONR Ice Mechanics initiative have provided opportunities for exploring this approach to remote sensing using both passive and active measurements. Passive sensing revealed significant spatial variability in the response of the ice to thermal stress. Detailed analysis of the acoustic signal in the water yields insight on the source mechanism, which included local uplift, subsequently verified by inspection of the fracture site. Flexural waves in the ice were anisotropically distributed with blocking by a nearby pressure ridge dominating the spatial variability. Variations in ice properties were also probed with artificial impacts on the ice surface, revealing significant variability in both shear and p-wave propagation. The influence of the pressure ridge was very marked in its attenuation of flexural waves, but significant modifications of shear and p-wave velocities were also measured. Finally, advantage was taken of an artificially induced fracture experiment conducted by Dempsey and Spencer in April 1993. Controlled fracturing was induced with a flat-jack leading to multiple acoustical and seismic emissions that were detected with a hydrophone array. Such measurements should provide a basis for comparison with models for the fracture of heterogeneous materials.
Monitoring thermal fracturing in ice: The relation to ice stress and strength
Authors: Stein P. J. , Lewis J. K. , Tucker W. B.
Published: October 2005

Here observations of thermally induced ice fracturing in the Arctic are summarized. Thermally induced fractures may be an important phenomena in understanding ice strength. Sets of observations of event locations using hydrophone and geophone arrays along with meteorological and ice stress measurements are discussed. Data are reviewed for both first and multiyear ice floes. Stress observations show that smooth first year ice can support much higher tensile forces. The event location data indicate that indeed first year ice is much less susceptible to thermal fracturing. This indicates that smooth first year ice is in some manner stronger than multiyear ice.
Acoustic field of Gaussian and Bessel transducers
Authors: Kiel/czyński P. , Pajewski W.
Published: October 2005

An explicit analytical form of the impulse response for circular transducer with truncated Gaussian distribution of vibrational velocity on its surface is developed. In an existing paper [J. Naze Tjotta and S. Tjotta, J. Acoust. Soc. Am. 71, 824 (1982)] the impulse response for Gaussian distribution was given [Eq. (17)]. This formula is valid only for the case of an ultrasonic transducer with infinite radius (a=+∞). In this paper an impulse response function for the case of truncated Gaussian profile is established. The formula [Eq. (3)] developed by the authors is valid for ultrasonic transducers of arbitrary radius a∈(0,+∞). Formula (17) from the above cited article by Naze Tjotta and Tjotta is a particular case of the more general formula [Eq. (3)] established in this paper. Employing the transfer function method, the acoustic field for truncated Gaussian distribution in the near and far zones is calculated. Similar calculations are performed for the circular transducer with truncated Bessel function distribution on its surface. The similarities and differences between these two kinds of acoustic fields are discussed.
Continuous field radiated by a geometrically focused transducer: Numerical investigation and comparison with an approximate model
Authors: Coulouvrat François
Published: October 2005

Spherical caps are widely used to produce efficiently focused ultrasonic fields. Due to the curvature of the source surface, no exact analytical expression of the radiated field is known. The approximate model of Williams and O’Neil [J. Acoust. Soc. Am. 17, 219-227 (1946); 21, 516–526 (1949)] is expected to be limited to high-frequency, slightly focusing sources. In order to determine more precisely the limits of that model, and to dispose of an efficient tool for describing precisely the focused field, a new numerical method is presented. It is based on two expansions of the pressure field into spherical harmonics in two conveniently chosen domains. The expansions are then matched. Validity of the method is assessed by making a comparison with the exact analytical solution for the planar case. Then, the sound field radiated by a sharply focusing radiator is investigated. Comparison of the results of the numerical procedure with the approximate model indicates a much wider domain of validity of the model than generally thought. More precise conditions for the applicability of the model are derived, that follows from simple considerations of geometrical acoustics.
Comments on ‘‘Ultrasonic scattering from spherical shells including viscous and thermal effects’’ [J. Acoust. Soc. Am. 93, 1687–1699 (1993)]
Authors: Hickling Robert
Published: October 2005

Further discussion is provided relating to a comparison made in the article by Anson and Chivers [J. Acoust. Soc. Am. 93, 1687–1966 (1993)].
Application of transient elastic waves to the nondestructive evaluation of plate structure with cavity or inclusion
Authors: Wu T.-T. , Gong J.-H.
Published: October 2005

This paper utilized the heterogeneous finite difference formulation to study the propagation of transient elastic waves in media with internal interfaces due to a steel ball impact. The media considered in this paper include a parallel layered half-plane, a dipping layered half-plane, and a plate with a hole or circular inclusion. Transient elastic waves generated by dropping a steel ball on the layered (both parallel and dipping) plates are recorded to check the validity of the results simulated from the present numerical scheme. In order to detect a void or inclusion in a plate structure, the near-offset seismogram and point-source/array-receiver (PS/AR) seismogram are simulated numerically. The simulated results of the near-offset seismogram suggested that the bottom-reflected P wave can be utilized to estimate the diameter of a circular inclusion. The unique features in the PS/AR seismogram suggested that the PS/AR seismogram can be utilized to identify a void or inclusion in plate structures. In combination with recent laser ultrasound developments, the present study can also serve as a basis for the detection of fine voids or inclusions in materials.
Echoes and helical surface waves on a finite elastic cylinder excited by sound pulses in water
Authors: Bao Xiao-Ling
Published: October 2005

The echo responses of a finite elastic circular cylinder, excited by obliquely incident sound waves in water, are difficult to analyze by exact theory. In this paper, an approximate theoretical model based on reradiation of the elastic helical surface waves is presented. The basic expressions, suitable in a certain range of angles of incidence, are derived to estimate the time sequence of echo pulses and the resonance modes of the cylinder. Experimental results are shown, and are compared with the calculated results of the time sequence of echo pulses; both are found to be basically in agreement with each other.
A composite randomization procedure for measuring spectral shape discrimination
Authors: Kidd Gerald , Dai Huanping
Published: October 2005

In studies of auditory profile analysis [D. M. Green, Profile Analysis: Auditory Intensity Discrimination (Oxford U. P., New York, 1988)], the sounds are presented at random levels to discourage the listener from basing the discrimination on a difference in absolute level rather than on a difference in the shape of the spectrum. A difference in absolute level, however, can still provide an effective discrimination cue if the difference is comparable to the range of randomization. Using enormous ranges of random levels is not desirable, because it is distracting to normal listeners and may exceed the dynamic range of hearing for listeners with hearing loss. This article describes a new experimental procedure which permits the experimenter to greatly reduce the range of level randomization in roving-level tasks.
Stimulus features affecting psychophysical detection thresholds for electrical stimulation of the cochlea. II: Frequency and interpulse interval
Authors: Pfingst Bryan E. , Morris Deborah J.
Published: October 2005

Psychophysical detection thresholds for electrical stimulation of the cochlea were measured in nonhuman primates (macaques) as part of a series of experiments exploring the stimulus features affecting detection. The monkeys were trained psychophysically using operant conditioning. One ear was treated with neomycin to destroy hair cells, and implanted with electrodes in the scala tympani and/or the cochlear wall. In experiment 1, detection thresholds were measured for trains of fixed-duration pulses and for sinusoids. For long-duration pulses (1 to 2 ms/phase), thresholds decreased as a function of frequency (pulse rate), reaching a minimum at a frequency between 125 and 210 pps, then increased as frequency was further increased. For shorter duration pulses, thresholds usually decreased monotonically as a function of frequency but sometimes showed a slight increase as a function of frequency near the highest frequencies tested. Typically slopes of the threshold versus frequency functions for fixed-duration pulses were equal to or less than slopes of threshold versus frequency functions for sinusoidal signals, where frequency and phase duration covaried. Additional observations on two of the cases were made in experiments 2 and 3. In experiment 2, thresholds for pairs of pulses were measured as a function of interpulse interval. Thresholds decreased as a function of interpulse interval up to intervals of 2 to 4 ms and then increased slightly. In experiment 3, thresholds were measured as a function of stimulus duration at two frequencies.

Thresholds decreased as a function of stimulus duration at a greater rate for the lower frequency pulse train, so that the difference between the detection thresholds for the two signals increased as a function of stimulus duration. These experiments suggest that stimulus frequency (i.e., repetition rate with phase duration fixed) is a significant contributor to the detection of electrical signals. This contribution may be due to a combination of effects of (a) increasing the number of neural responses to the stimulus as frequency is increased, and (b) temporal interactions of those responses, as interpulse intervals become small, due to refractory periods or other periods of altered excitability that follow a pulse.
The relationship between sound transfer functions from free sound field to the eardrum and temporary threshold shift
Authors: Hellström Per-Anders
Published: October 2005

Three groups of 12 subjects were utilized for an experiment in which the temporary threshold shift due to a free-field exposure was measured and compared to the sound transfer functions from free-sound field to the subjects’ eardrums. Subject selection was based upon their sound transfer functions and the requirement of normal hearing. The subjects were assigned to one of three groups depending on their dominantly sound transfer function frequency: Low, middle, or high. A probe tube with a miniature microphone was used for the measurement of the sound transfer functions in 1/3-oct bands. The measurements were performed in frequency bands from 0.2 to 20 kHz with one direction of sound incidence: 0° azimuth and 0° elevation. The subjects were exposed twice to a 2-kHz and twice to a 4-kHz narrow-band noise monotonically on four different occasions. Pre- and postexposure sweep Békésy audiograms were recorded and the temporary threshold shift calculated as the difference between the two. The averaged temporary threshold shifts differed significantly among groups.
Further evidence for an autonomous processing of pitch in auditory short-term memory
Authors: Semal Catherine , Demany Laurent
Published: October 2005

In four related experiments, subjects had to discriminate between the presence or absence of a frequency difference between two pure tones separated by 4.3 s. The interference effects of other tones (I), inserted during the retention interval, were investigated. A previous study [C. Semal and L. Demany, J. Acoust. Soc. Am. 89, 2404–2410 (1991)] had shown that subjects’ performance strongly depended on the pitch relations between the test tones and the I tones, but not on the spectral composition of the I tones. This suggested that the mnemonic system processing pitch is deaf to sharpness of timbre. In the present study, the I tones could differ or not from the test tones in intensity (by ±6 or 15 dB) or in amplitude envelope (periodic as well as aperiodic envelopes were used). It was found that such differences had very little effect on performance, suggesting that the mnemonic system processing pitch is deaf to loudness and to dynamic aspects of timbre. However, for I tones with a dense spectrum in the vicinity of the test tones’ frequencies, widening the I tones’ spectrum improved performance, probably because this spectral widening decreased the salience of the I tones’ pitches.
A hybrid target motion analysis/matched-field processing localization method
Authors: Fawcett John A. , Maranda Brian H.
Published: October 2005

A passive localization method is described that combines the localization features of target motion analysis and matched-field processing. This method works directly with complex-valued beam spectra as its input. The algorithm can handle weak or fading signals and, because of its long-term integration of power from the matched-field processor, has enhanced detection characteristics. In towed array applications, this hybrid algorithm combines the broadside localization performance of target motion analysis with the good end-fire performance of matched-field processing to give good all-around performance.
Localization of a maneuvering target using simulated annealing
Authors: Maranda Brian H. , Fawcett John A.
Published: October 2005

A two-stage algorithm is described for passively localizing a maneuvering target with a towed array sonar. The first stage of the algorithm uses simulated annealing to obtain an initial estimate of the target track; the second stage applies a modified Newton’s method to this initial estimate in order to find the final track estimate. It is shown, using simulated examples, that a maneuvering target with a low signal-to-noise ratio can be successfully localized by this technique.
An approximate expression for the Cramér–Rao bound on direction-of-arrival estimation with small ring arrays
Authors: Swingler D. N.
Published: October 2005

It is demonstrated that the Cramér–Rao lower bound on direction-of-arrival estimation with two uncorrelated but closely spaced narrow-band sources impinging on a small circular array is well approximated by a modification of a recently published, extremely simple, nonmatrix, line-array formula. The approximation is demonstrated to be useful for a number of sensors from about 5 to 30, SNR’s from −30 to +30 dB, source separations down to about 0.1 beamwidths, and radius-to-wavelength ratios from 0.1 to 2. The rms error is about 30%.
Results of using an artificial neural network to distinguish single echoes from multiple sonar echoes
Authors: Chang W. , Bosworth B. , Carter G. Clifford
Published: October 2005

Empirical results illustrate the pitfalls of applying an artificial neural network (ANN) to classifying underwater active sonar returns. During training, a back propagation ANN classifier ‘‘learns’’ to recognize two classes of reflected active sonar waveforms. Waveforms in class 1 have two major sonar echoes or peaks. Waveforms in class 2 have one major echo or peak. Our results show how the classifier ‘‘learns’’ to distinguish between the two classes. Testing the ANN classifier with different waveforms having one major peak, and waveforms having two major peaks generated unexpected results: The number of echo peaks was not the feature used to separate classes.
Quadrupole directivity of jet noise when impinging on a large rigid plate
Authors: Shen Jianping , Meecham William C.
Published: October 2005

The aerodynamic sound generated by a subsonic jet normally and obliquely impinging on a large, rigid, flat plate was studied at the Aerosonics Laboratory at UCLA. Correlation techniques were used to focus on source regions and to discriminate against such signals as reflections. Correlations between the signals from both the surface transducers on the plate and hot-wire sensors near the plate, and far-field microphone signals were measured at different jet speeds (Mach number=0.3–0.9), nozzle sizes (1, 11/4, and 11/2 in.), nozzle-to-plate distances (3–22 nozzle-diameters) and impinging angles (0°, 15°, and 30°). For each case, the microphone was placed at several locations around the jet, so that the directivity pattern was obtained. The directivity results showed that the correlation approach resulted in quadrupolelike directivity patterns, suggesting such sources with approximately fixed orientation. The sound intensity had a minimum at around 45° around the plate normal, independent of the impinging angle. This is the only instance of directly observed quadrupole patterns (four-leafed clover) for free jets which the authors know of. Correlation techniques are required, or else the sources overlap the directivity patterns and nearly smear out the maxima and minima.