bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of amplitude modulation on profile detection using multiple short signals
Authors: Smith Michael A. , Bacon Sid P.
Published: October 2005

The detection of an increment in a target component is more difficult when the surrounding, nontarget components are sinusoidally amplitude modulated [H. Dai and D. Green, J. Acoust. Soc. Am. 90, 836–845 (1991)]. The purpose of the present study was to determine whether the detrimental effects of amplitude modulation (AM) on profile analysis could be eliminated by providing a relatively ‘‘static’’ profile during the course of AM. The task was to detect an increment in a 1-kHz target component that was centered in a complex containing 21 logarithmically spaced components ranging in frequency from 200 to 5000 Hz. The target component was always unmodulated whereas the nontarget components were either unmodulated or sinusoidally amplitude modulated at a rate of 10 Hz. The signal was composed of multiple 20-ms presentations, all positioned at successive peaks, valleys, or leading edges of the modulation cycle. As in previous work with longer signals, thresholds generally increased with increasing modulation depth. An attempt to account for the effects of AM in terms of the short-term pedestal resulting from the modulation was only marginally successful. [Work supported by NIH and Sigma Xi.]
Analysis of a thermoacoustics prime mover above onset of self-oscillation
Authors: Larraza Andrés , Atchley Anthony A.
Published: October 2005

Nonlinear effects that lead to amplitude saturation in a thermoacoustic prime mover, are described. The evolution of the acoustic amplitude is described by a homogeneous Ginzburg equation of the form dA/dt=αA−βA2. The linear term represents the contribution from the power output due to the temperature gradient and viscous and thermal losses. The coefficient α is positive above onset. The cubic term is a consequence of the nonlinear induced vorticity at the boundary layer that originates from irreversible terms. In the approximation considered, the coefficient β is positive and a steady state results from the balance between the linear growth and the nonlinear saturation. The steady-state amplitudes are in qualitative agreement with observations made by Wheatley [Frontiers in Physical Acoustics, Varena (1986)] and Hofler etal. [see abstract in this session]. Observations made by Swift [J. Acoust. Soc. Am. 92, 1551 (1992)] on the dependence of acoustic pressure versus heater power are also in qualitative agreement with the theory. [Work supported by ONR and NPS Direct-Funding Program.]
Thermoacoustic termination for a traveling wave tube
Authors: Kordomenos John N. , Atchley Anthony A. , Raspet Richard , Bass Henry E.
Published: October 2005

A theory for thermoacoustics of traveling waves has been developed and presented previously by Raspet etal. [J. Acoust. Soc. Am. 93, 2278 (A) (1993)]. In this paper, experimental results are compared with predictions of this theory. The experiment consisted of measuring the pressure reflection coefficient of a thermoacoustic termination located at one end of a 20-m-long, 5-cm-i.d. tube. The termination consisted of a hot heat exchanger, a 5-cm-long, square pore stack, a cold heat exchanger, and a cold end. The temperature of the hot heat exchanger was maintained near room temperature. The temperature of the cold end was held close to liquid nitrogen temperature (−77 K). Measurements were made for frequencies ranging from 300 to 1200 Hz, and for different cold end impedances. There is good agreement between the measured and predicted results. [This work was supported by the Office of Naval Research.]
Cooling effect introduced by acoustic streaming
Authors: Wu Junru , Winkler Andrew J. , O’Neill Timothy P.
Published: October 2005

It is believed that a fetal exposure to focused ultrasound during the second and third trimesters of pregnancy represents one of the worst-case situations for thermal effects introduced by ultrasound. This is because (1) the ultrasound beam may pass through a distended bladder that is filled with low attenuating fluid, and (2) heating effects may be most pronounced near well-ossified bone of high attenuation coefficient. It was found in recent invitro experiments that acoustic streaming in low attenuating fluid may dramatically reduce the temperature rise generated by ultrasound at the surface of bone if the ultrasound path contains a low-attenuating-fluid/thin-soft-tissue/bond structure. [Work supported by Hewlett-Packard Co.]
Convective heat transfer from a sphere due to acoustic streaming
Authors: Gopinath Ashok , Mills Anthony F.
Published: October 2005

Convective heat transfer from a rigid sphere due to acoustic streaming is discussed for large streaming Reynolds numbers. The work is motivated by a need for the thermal analysis of the experiments on containerless materials processing using acoustic levitation. The acoustic signals used in these experiments give rise to a strong steady fluid motion around levitated alloy samples. The associated convective heat transfer rates are significant enough to give rise to heating/cooling rates in the samples which are crucial in determining their material structure and hence their thermophysical properties. The steady heat transport effect due to the streaming motion is studied with the levitated sample modeled as an isolated solid sphere in a pure plane standing sound field. Strong acoustic signals in the range of 150–170 dB and 1–2 kHz are considered. Analytical and numerical solution techniques are used to obtain a Nusselt number correlation for the heat transfer when the surrounding fluid is a gas with Prandtl number ∼O(1). A simple experiment performed to confirm some of the predictions is found to give very good agreement with the analysis. A more detailed report of the results of this study may be found elsewhere [J. Heat Transfer 115, 332–341 (1993)]. [Work supported by NSF Grant No. CTS-8918777 and the NRC.]
Preliminary investigation of high amplitude standing waves with laser Doppler velocimetry
Authors: Corrigan Timothy J. , Atchley Anthony A.
Published: October 2005

A previous study of thermoacoustic heat transport phenomena [Atchley etal., J. Acoust. Soc. Am. 88, 251–263 (1990)] reported measurements of the acoustically induced temperature difference ΔT generated across short, poorly thermally conducting plates situated in high amplitude acoustic standing waves. That study focused on the dependence of ΔT on the position of the plates in the standing wave. Significant discrepancies between the predicted and measured results were observed at high acoustic pressure amplitudes. Moreover, for a given mean gas pressure, there was a threshold acoustic pressure amplitude above which irregularities appeared in the plots of ΔT vs kx. There was evidence that some velocity-dependent effect might be the cause of the discrepancies. An investigation of the acoustic velocity field in high amplitude standing waves has been initiated to determine whether there are measurable irregularities in the velocity field that can account for the observed behavior. Preliminary results of this investigation are reported. [Work supported by the Office of Naval Research.]
On statistical fluctuations in single scattering by an ensemble of scatterers
Authors: Goedecke George H. , De Antonio Michael , Auvermann Harry J.
Published: October 2005

Expressions in terms of the presumed known scattering cross section of the objects are derived for the ensemble average single scattering differential cross section σ̄N and its rms deviation ΔσN due to a homogeneous ensemble of N identical objects randomly positioned with no corrections in an observed volume V. For wavelength λ, it is well known that, if Nλ3/V≤1, there is considerable diffuse scattering, while, if Nλ3/V≳≳≳1, the scattering is essentially forward and coherent. Apparently not so well known is the result of ΔσN/σ̄N depends on another parameter α≡C(θ)N(λ3/V)4/3, when C(θ) is a numeric of order unity and depends on scattering angle θ. It is shown that, if α≫1, then ΔσN/σ̄NαN−1/2 and is very small, while if α≤1, then ΔσN≊σ̄N. Application involving numerical simulation is made to single scattering of acoustic waves by an ensemble of turbules.
The FDTD method for ultrasound pulse propagation through a two-dimensional model of the human breast
Authors: Manry Charles W. , Broschat Shira L.
Published: October 2005

The incidence of breast cancer is increasing. In 1961 a woman had a 1 in 20 change of getting breast cancer; today it is 1 in 9. The earlier a tumor is detected, the more likely the survival of the victim. Thus it is critical that high-resolution breast imaging techniques be developed that are capable of detecting small tumors. One modality under consideration is ultrasound imaging. Algorithms developed for ultrasound imaging usually assume that scattering of energy in the breast is weak, allowing simple and efficient image formation algorithms. However, experiments conducted at the University of Pennsylvania suggest that fat lobes near the breast’s surface refract ultrasound energy as it passes through the breast. This strong refraction violates the weak scattering assumption and calls into question the validity of algorithms using this approximation. A higher-order finite-difference time-domain (FDTD) algorithm has been developed that can be used to model the effects of fat lobes on the propagation and scattering of an ultrasound pulse in the human breast. The simple breast model used is two-dimensional with a fat structure similar to that of the Pennsylvania study. Results support the conclusion that refraction in the breast poses a significant challenge to ultrasound imaging. [Work supported by NSF.]
Speech perception
Authors: Kuhl Patricia K.
Published: October 2005

In this tutorial review new concepts and experimental results on speech perception, particularly its development, will be described. First, an overview is provided of the results of classical experiments investigating speech preception in its ‘‘initial state.’’ Next, new results demonstrating the effects of language experience on speech preception will be described, showing that the preception of speech is altered by exposure to language in the first 6 months of life. Finally, preception of auditory-visual illusions in speech preception will be described, including a 90-s demonstration experiment that allows audience members to experience the effect. Auditory-visual effects are discussed within the context of speech perception–production links which have their inception in early infancy. A new theory of the development of speech perception that incorporates these results will be presented.
Tomographic measurements of frontal variability in the Barents Sea
Authors: Chiu Ching-Sang , Miller James H. , Lynch James F.
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 objective of the experiment was to map and study the oscillations of the Barents Sea Polar Front using acoustic tomography coupled with traditional hydrographic techniques. Because mesoscale ocean variability has shorter spatial and temporal scales in a coastal environment, a vertical receiving array and frequently transmitting tomography sound sources were used to achieve an enhanced system resolution appropriate for coastal monitoring. The vertical array data were processed using plane-wave beamforming to separate ray arrivals in both time and angle. In addition, modal arrivals were separated using broadband modal beamforming techniques. The processed travel time data were then ‘‘inverted’’ using a hybrid ray-mode inverse technique to produce a time series of maps of the polar front. In this presentation, the hybrid ray-mode inverse method and the frontal variability as imaged by this shallow-water tomography system are discussed. [Work supported by ONR 1125AR.]
Identification and arrival time estimation of bandpass modes and rays for acoustic tomography in the Barents Sea using a vertical array
Authors: Miller James H. , Chiu Ching-Sang , Lynch James F. , McLaughlin Philip , Miller Christopher W. , Von Der Heydt Keith , Kemp John
Published: October 2005

In the 1992 Barents Sea Polar Front Experiment, bandpass acoustic tomography signals centered at 224 Hz were received with very high SNR on a 16-element vertical hydrophone array at a range of 35 km from the source. The depth of the ocean varied from 120 m at the source to 280 m at the vertical array. A critical part of travel time tomography is the measurement of the arrival time of individual modes and rays. Identifying and tracking these mode and rays can be extremely difficult using a single hydrophone in coastal waters due to signal interference. A vertical array has the potential to solve these problems. An efficient signal processing scheme is described, written in MATLAB, that simultaneously (1) beamforms for the bandpass modes or rays, (2) compensates for clock drift, sampling skew, and array tilt, and (3) compresses the maximal-length, phase-encoded signal. Data are presented that show that the beamforming along with acoustic modeling provides identification of the arrivals with a high degree of confidence. Errors in measuring the arrival times are estimated to range from 2 ms for low modes to 10 ms for high angle rays making the arrivals useful for inversions. [Work supported by ONR, Code 1125AR.]
Sound in the meeting room—A listener’s perspective
Authors: Pope J.
Published: October 2005

While careful attention is given to the visual appearance of most meeting spaces, the aural appearance often is neglected. Meeting rooms serve a multiplicity of functions in a variety of configurations. Typical of rooms at Acoustical Society meetings, for example, is a lecture-style setup with a presenter at the front of the room addressing an audience of 30–300 listeners. A good room will facilitate the communication of the presenter’s message. The listener perceives, comfortably, only what the presenter wants heard. In practice, a number of acoustical defects and distractions may exist. Problem areas include air-handling (HVAC) noise, sound transmission from adjacent spaces, inappropriate reverberation, noise from audio-visual presentation equipment, and audience-generated noise. In addition to bad luck, the causes appear to include design, construction, maintenance, meeting planning, and facility staff issues. The use of a sound reinforcement system can mitigate some problems, while introducing new ones. The intent of this paper is to raise questions for discussion, and to provide an introduction to the session.
Measurements of bi-static scattering coefficients with frequency dispersive source arrays
Authors: Booth Newell O. , Sullivan Shelby F.
Published: October 2005

A method of measuring bi-static scattering coefficients with frequency dispersive source (FDS) arrays is described and illustrated with experimental data. FDS array pings form a set of narrow beams at different frequencies. Signals from vertical FDS arrays are scattered from boundaries and received on a bi-static receiver. Resolution of the scattering area is achieved from the intersection of the time of arrival ellipse and the conical beam. FDS arrays design principles are summarized and efficient methods of analyzing the data using reverberation models are described.
Elastic wave scattering by an elliptical inclusion in a fluid-saturated porous medium
Authors: Gurevich Boris , Sadovnichaja Ada P. , Lopatnikov Sergei L. , Shapiro Sergei A.
Published: October 2005

The problem of the scattering of an elastic wave by a small (compared to the wavelength of the fast compressional wave) elliptical porous inclusion placed in another fluid-saturated porous medium is studied using the Born approximation. The mechanical behavior of both host and inclusion materials is described by the low-frequency version of Biot’s theory. Explicit formulas for the amplitudes of the scattered normal compressional and shear waves and of Biot’s slow compressional wave are obtained. The effectiveness of Biot’s slow wave generation depends essentially on the ratio of the wavelength of the slow compressional wave to the inhomogeneity size. For large values of this ratio the results agree with the earlier low-frequency results [J. G. Berryman, J. Math. Phys. 26, 1408–1419 (1985)] derived for a spherical inclusion. In the opposite case new results are obtained. They are used to estimate the effective velocity and attenuation of the normal compressional wave in a porous medium containing randomly distributed inclusions. The frequency dependence of the attenuation is consistent with the results for randomly layered porous materials.
Higher-order perturbation theory versus the scattering operator expansion method for 3-D surface scattering
Authors: Dubberley John , Novarini Jorge , Keiffer Richard
Published: October 2005

To this point little work available in the literature has examined whether three-dimensional scattering events can be successfully modeled by a two-dimensional stimulation. This has mainly been caused by a lack of sufficient computational and modeling power in the past. A contributing reason to the low interest in the validity of this assumption is that there seems to be no compelling reason why the two-dimensional assumption would fail to correctly approximate the three-dimensional situation. However, in the interest of completeness, the ramifications of this assumption must be explored. Here two models are used to provide a preliminary look at this issue. Perturbation theory and the scattering operator expansion surface scattering methods will be compared to each other over a variety of canonical and ‘‘realistic’’ surfaces. The strengths and weaknesses of each model for this task will be mentioned. Up to third-order implementations of these methods will be used.
Performance of a thermoacoustic refrigerator with an improved stack geometry
Authors: Hofler Thomas J. , Adeff Jay A.
Published: October 2005

The original Hofler thermoacoustic refrigerator is improved by means of a two-segment stack. Each segment of the stack can have a different layer separation that is approximately best for its local acoustic environment and heat load. A few different combinations of stack segments were tested experimentally. The best data indicated an increase in temperature span from 102 to 118 °C, and an increase in COP relative to Carnot of about 40%, compared to the best single-stack element.
CFC-free refrigeration: Thermoacoustic technology-design, construction, and evaluation
Authors: Salyards Joseph Paul
Published: October 2005

Environmental priorities are forcing chlorofluorocarbons (CFC’s) out of the marketplace thereby creating a new demand for cooling technologies. The primary objective of this study was to design, construct, and evaluate a CFC-free refrigeration system. A prototype thermoacoustic (TAC) system utilizing high-amplitude sound waves in an inert gas was developed, and several designs were evaluated. The TAC system showed potential as an alternative refrigeration method with the optimum design resulting in a 42.2 °F drop in ambient air temperature. Potential applications exist in refrigeration and air-conditioning; the cooling of satellite-borne sensors; and as either a heat-driven sonar source, cryogenic refrigeration unit, or electric generator.
Arctic ambient noise and climate change
Authors: Denner Warren W.
Published: October 2005

In global warming, sea ice plays a significant role, and sea ice conditions may provide one of the most sensitive parameters to monitor. Modeling predicts that warming will be greatest at high latitude, and sea ice properties are very sensitive to warming and changes in atmospheric forcing. Therefore, sea ice might provide a sensitive marker for climate change. The mechanical properties of sea ice are related to the ice temperature, salinity, thickness, concentration, and flow size distribution. It has been established that the ambient noise field under pack ice is correlated to the mechanical properties, ice conditions, and forcing. Many studies over the last two decades have delineated some of these relationships. The hypothesis of this paper is that monitoring the ambient noise under the ice, for which there is well-developed and reliable technology, may be an excellent way to detect a climate change signal. This paper will review the relationships between under ice ambient noise and the properties of the ice pack. Based on what is known, a monitoring system consisting of remotely operated buoys is proposed. A proposed buoy design and sampling array for the Arctic is presented. Used in conjunction with satellite remote sensing, the system could provide for continuous monitoring of the ice pack for other purposes and would be cost effective for acoustic monitoring of the climate change signal in the Arctic.
Oceanological aspects of acoustic monitoring of Arctic Ocean climate
Authors: Sabinin K. D. , Pisarev S. V.
Published: October 2005

The Arctic Ocean is an important object of investigation in the global ATOC program because of its crucial role in the heat balance of the Northern Hemisphere. Although the temporal and spatial variability of the sound speed in the Arctic Ocean is relatively weak, the Arctic ice cover essentially complicates modeling of the acoustic response to climate change. Moreover, the influence of the strongly varying ice cover causes additional difficulties in interpretation of the results of acoustic ocean thermometry for several reasons: (1) the extremely strong influence of ice distribution on the ocean–atmosphere heat exchange, (2) the long-term variation of the ice cover, and (3) the specific response of the surface water sound speed to heating of an ice-covered sea (a heat input should decrease the sound speed under melting ice). Under-ice winter convection can also create specific kinds of inhomogeneities of the Arctic Ocean (chimneys, plumes of dense water, etc.). Additional serious difficulties arise because of strong dependency of Arctic climate on the heat inflow of both the Atlantic and Pacific Oceans. This changeable inflow can cause long-term variations of the Arctic Ocean. It seems worthwhile to begin the Arctic ATOC with the installation of acoustic tracks across the Fram Strait.
Voice simulation with a three-mass model of the vocal folds
Authors: Story Brad H. , Titze Ingo R.
Published: October 2005

The classic two-mass model of the vocal folds [K. Ishizaka and J. L. Flanagan, Bell Syst. Tech. J. 51, 1233–1268 (1972)] has been extended to a three-mass model in order to represent more accurately the body-cover vocal fold structure [M. Hirano, Folia Phoniat. 26, 89–94 (1974)]. The model consists of two ‘‘cover’’ masses that are coupled to a ‘‘body’’ mass by nonlinear springs and viscous damping elements. The body mass, which represents muscle tissue, is also coupled to a rigid wall (assumed to represent the rigid laryngeal framework) by a nonlinear spring and damping element. The two cover springs are intended to represent the vocal ligament tension while the body spring simulates the tension produced by contraction of the thyroarytenoid muscle (TA). Additionally the two cover masses are coupled to each other through a linear spring that can be regarded as representing the surface tension of the cover and hence largely contributes to the mucosal wave velocity. Effects on the vocal fold movement due to changes in subglottal pressure, spring tensions, element masses, and vocal tract loading will be shown.
Phonation threshold pressure in a physical model of the vocal folds
Authors: Titze Ingo R. , Titze Michael R.
Published: October 2005

A physical model of a vocal fold was constructed with three layers: an artificial epithelium (latex), a superficial Reinke’s space (water), and an immobile vocal fold body (aluminum). This vocal fold was positioned in a plexiglas airway such that the glottal aperture and the convergence angle could be varied systematically with respect to a solid boundary, which represented the opposite vocal fold in a hemilarynx configuration. Subglottal pressure was controlled with a constant pressure valving system. Phonation threshold pressure (the Hopf bifurcation in nonlinear dynamics) was measured as a function of glottal aperture and divergence angle. This pressure increases with increased aperture and convergence, as predicted by theory, but results for a divergent glottis are not as easy to interpret. [This research was supported by Grant No. P60 DC00976 from the National Institute on Deafness and Other Communication Disorders.]
Laryngeal resistance of an in vivo canine model of phonation with a constant air pressure source
Authors: Nasri Sina , Namazie Ali , Ye Ming , Sercarz Joel A. , Kreiman Jody , Gerratt Bruce R. , Berke Gerald S.
Published: October 2005

Previous studies of laryngeal biomechanics using invivo models have generally used a constant air flow source. Several authors have recently suggested that during phonation, the lung–thorax system functions as a constant pressure source. The present paper describes an invivo canine system designed to maintain a constant peak subglottic pressure (Psub) using a pressure-controlling mechanism. It was found that with a decrease in Psub, the range of recurrent laryngeal nerve stimulation (RLNS) voltage needed to induce phonation was reduced. At a given superior laryngeal nerve stimulation (SLNS) level and Psub, increasing levels of RLNS resulted in a normal distribution of vocal efficiencies. For each SLNS and Psub, minimum and maximum levels of RLNS were determined outside of which no phonation was possible. Levels of RLNS that produced an optimal stable phonation were also identified. Increasing levels of RLNS resulted in significant decreases in glottal air flow. Contrary to a previous report using a constant flow source, increasing levels of SLNS produced a significant decrease in glottal resistance. This is consistent with another previous study [D. M. Moore and G. S. Berke, J. Acoust. Soc. Am. 83, 705–714 (1988)] demonstrating that the open quotient increased with increasing SLNS.
A study of pulsatile airflow in the excised larynx model
Authors: Alipour Fariborz , Scherer Ronald C.
Published: October 2005

The pulsatile airflow in the excised larynx was investigated with the simultaneous measurements of glottal pressure, volume flow, EGG, and particle velocity at various dynamic conditions of the larynx. Canine larynges were mounted in a bench with some sutures attached to cartilages to mimic the function of laryngeal muscles. The sustained oscillations were obtained and maintained with the flow of heated and humidified air through the trachea. The pitch and amplitude of oscillations were controlled with amount of airflow and the mechanical adjustment of glottal adduction and vocal-fold elongation. The particle velocity was measured above the glottis with a constant temperature hot-wire probe at various locations and oscillating conditions. The measured subglottal pressure with a pressure transducer had a periodic variation and its mean value was higher than the manometer’s reading of the same location. The measured particle velocity showed some turbulence superimposed on a periodic flow. The mean particle velocity showed some variations in the glottal exit area both along the vocal folds and across the glottis. [Work supported by NIDCD Grant No. DC00831-02.]
Formant sensitivity in the vocal tract
Authors: Lee Sungbok
Published: October 2005

Sensitivity of formants to perturbations of the location and degree of tongue constriction was studied. These two tongue parameters were extracted from vowel-like midsagittal tongue shapes (N=321) generated using a tongue model [Harshman etal., J. Acoust. Soc. Am. 62, 693–707 (1977)]. The tongue shape data were arranged such that the tongue parameters vary montonically. Lip opening was varied from 0.3 to 6.0 cm2 in 0.3-cm2 steps and the first three formants of each vocal tract were computed. Formant sensitivity was evaluated as dF/dA (Hz/mm), where dA is perturbation in a tongue parameter and dF is the corresponding formant change, and was plotted as a function of the location of tongue constriction. The results can be interpreted in terms of the formant variability, or stability, of a given vocal tract configuration. One finding is that at the tongue position associated with the vowel /u/ the formants are very stable under perturbation of the location of constriction. However, the same position is found to be the most unstable position for both F2 and F3 under perturbation of the degree of constriction. This may explain the largest F2 and F3 variations of /u/ in a set of normalized production data of vowels [Syrdal and Gopal, J. Acoust. Soc. Am. 79, 1086–1100 (1986)]. [Work supported by NIDCD, DC 00296.]
Gradation of jaw perturbation effects on mandibular, labial, and velar kinematics
Authors: Kollia H. Betty
Published: October 2005

It was recently shown that anatomically linked and remote articulators such as the jaw, the lips, and the velum are functionally constrained during bilabial closing, exhibiting temporal stability in the patterns of interarticulatory cohesion [Kollia etal., J. Acoust. Soc. Am. 92, 2390 (A) (1992)]. Further, it was found that, when functionally related for speech, jaw, lips, and velum show compensatory kinematic adjustments to a mechanical jaw perturbation, such as increased movement displacement and oral closing velocity, thereby maintaining interarticulator cohesion [Kollia etal., J. Acoust. Soc. Am. 91, 2474 (A) (1992)]. The interpretation is that speech movements are controlled in a global manner, rather than independently, reflecting large scale vocal tract actions. The present study aims at untangling the gradient effects of the perturbation on the articulators and their kinematic parameters. Overall load effects depended on the distance of the articulator from the site of the perturbation. Load effects were heightened in structures that were more proximal to the perturbation such as the jaw and the lower lip, and diminished in more remote structures, such as the upper lip and the velum. Moreover, load effects depended on the load onset time and had a variable effect on the different kinematic parameters. [Work supported by NIH Grant Nos. DC-00121 and DC-00594 to Haskins Laboratories.]
Measurement of large scale deformation of the Arctic ice pack using acoustic backscatter
Authors: Duckworth Greg , LePage Kevin , Farrell Ted
Published: October 2005

The ONR AEAS Program sponsored a low-frequency reverberation study program in the Central Arctic as part of the AREA-92 Exercise in March–April of 1992. The ZIRCON ice camp was the site of the monostatic and bistatic active sonar experiment with acoustic sources, a 256-channel billboard receive array, and real-time processing and display system. The reverberation data collected have been coherently processed between sequential pings to estimate the bearing, range, and radial velocity of ice scattering footprints of various range and bearing extents. Due to the highly repeatable nature of reverberation from the ice canopy, high source strength, and the gain of the receiver array, this processing is shown to be capable of unambiguously estimating the movement of these footprints over a 250-km-radius area to better than 10-m accuracy for transmissions as far apart as 4 h. Strain rate estimates using the technique agree with sparse GPS data in the area covered, and are shown to be well modeled by a simple three-parameter strain rate field. The details of the output from the processing also shed light on the fundamental acoustic propagation and backscatter processes themselves. [Work supported by ONR.]
Long-range measurements of the strength and spectral character of low-frequency surface reverberation
Authors: Gauss Roger C. , Soukup Raymond J. , Fromm David M. , Fialkowski Joseph M.
Published: October 2005

Long-range monostatic measurements of low-frequency (185–985 Hz) and low-grazing-angle (nominally 5–15 deg) acoustic surface scattering were made in the Gulf of Alaska in February of 1992. The upward-refracting sound-speed profiles permitted ensonification of the sea surface at ranges of several tens of kilometers without interacting with the ocean bottom. Reverberation returns from these ranges were used to quantify both the strength and spectral character of surface/near-surface reverberation as functions of frequency and environmental conditions. Spectral results over the range of wind speeds (4–17 m/s) have revealed a dominant zero-Doppler component and a weaker-than-expected dependence of spread on both wind speed and frequency. Overall, the results are consistent with sub-surface bubbles as the driver for surface reverberation when whitecaps are present, and will provide data for comparison with theoretical and numerical models, which in turn will give insight into the physical mechanisms responsible for the observed acoustic scattering. [Work supported by SPAWAR (PMW-182) and ONR (Code 4532).]
Oceanographic inferences from ambient noise in the marginal ice zone
Authors: Buckingham Michael J.
Published: October 2005

In the polar seas the spatial structure of the ambient noise is often determined by the upward refracting sound-speed profile. Such a profile supports normal modes, even in the absence of bottom interactions. A full theoretical (analytical) model of ambient noise in an inverse-square profile—representative of polar waters—has been developed [Buckingham, Philos. Trans. R. Soc. (in press)], which yields expressions for the auto and cross spectral densities of the noise that are valid at infrasonic frequencies (VLF) and low frequencies (LF) up to several kilohertz. Three terms appear in these expressions, representing the modal and continuous components of the noise. When the theoretical spectra are compared with ambient noise data taken in the marginal ice zone off the east coast of Greenland, a crude distribution of noise sources at the ice edge can be inferred and bottom effects in the observed spectra become apparent. The spatial inhomogeneity of the noise is also very evident from the theory, which has implications concerning beamforming for obtaining noise directionality information. [Research supported by ONR.]
Acoustical determination of the ice growth in the Arctic
Authors: Laible Henry A. , Rajan S.
Published: October 2005

A crosshole tomography experiment was conducted in the Arctic between April 1992 and March 1993 to determine the time evolution of the acoustic/elastic properties of sea ice. Data were taken every third day for 9 months using an array of vertical and horizontal transducers located in the ice and water column below the ice. A method to monitor the growth of the underside of the ice consisted of comparing the arrival times of both the direct path and reflected path from transmitters in the water column to the receivers in the water column. The differences in arrival times over the 9 months indicates as much as 1-m growth of ice. In addition to the ice growth estimates, the reflection coefficient was determined as a function of time and angle. Acoustic characteristics of the ice in the skeletal layer at the ice/water interface was also estimated.
Performance of shaded, rectangular hydrophones in the reduction of turbulent flow noisea)
Authors: Ko Sung H.
Published: October 2005

Turbulent boundary layer pressure fluctuations can be reduced by filtering either a wave number through a finite hydrophone or a hydrophone array or by filtering the wave number through an elastomer layer. In general practice, various configurations of hydrophone arrays are embedded within a layer of elastomer, thus reducing the turbulent boundary layer pressure fluctuations. The theoretical model considered in this paper is a plane elastomer layer backed by an infinitely rigid surface; the other side of the layer is exposed to turbulent flow. This paper examines the performance of shaded, rectangular hydrophones for the flow noise reduction. The rectangular hydrophone is shaded with a triangular, semicircular, or cosine weighting function in the flow direction. Numerical calculations were made for both flush-mounted and embedded hydrophones. The results presented are comparisons of numerically calculated noise reductions between shaded and unshaded hydrophones.
Limited resolution of spectral contrast and hearing loss for speech in noise
Authors: ter Keurs Mariken , Festen Joost M. , Plomp Reinier
Published: October 2005

This paper examines the relations among the spectral contrast needed for speech intelligibility, hearing loss for speech in noise, and auditory filter bandwidth. Fifteen hearing-impaired listeners with relatively flat, mild-to-moderate sensorineural losses and eight normal-hearing listeners participated in the study. The spectral contrast needed for speech intelligibility was determined by reducing spectral contrast in the speech signal and measuring the reduction in contrast beyond which the speech-reception threshold (SRT) for sentences in noise increases. Reduction of spectral contrast was accomplished by smearing the envelope of the squared short-time fast Fourier transform by a convolution with a Gaussian-shaped filter, and overlapping additions to reconstruct a continuous signal. Auditory filter bandwidth was determined by estimating auditory filter shapes at center frequencies of 0.8, 1.6, and 3.2 kHz, using a notched-noise masking paradigm. The results show that limited resolution of spectral contrast is only loosely associated with hearing loss for speech in noise. Moreover, the correlations between the SRT for unsmeared speech and the auditory filter bandwidth at various frequencies were weak.
Measuring human cochlear traveling wave delay using distortion product emission phase responses
Authors: Kimberley Barry P. , Brown David K. , Eggermont Jos J.
Published: October 2005

A method is presented here in which cochlear traveling wave delays are estimated through the measurement of distortion product emission phase (DPE) responses. This method assumes that the site of generation of DPEs is at the f2 place. Eighteen adult female and 18 adult male human ears, all with normal hearing, underwent DPE testing. For each ear, DPE phase responses were computed for eight values of f2 varying from 10 to 0.78 kHz. Linear DPE phase versus DPE frequency relationships were found. Estimates of traveling wave delay from the ear canal to the f2 place varied from about 1 ms for the 10-kHz place to 3.5 ms for the 0.78-kHz place. These estimates agree well with previous traveling wave delay estimates using electrocochleography. Test–retest comparisons of delay estimates were generally within 0.25 ms. In addition, within-subject interaural delay differences were smaller than between-subject interaural differences. Within-subject interaural delay differences were generally less than 0.5 ms. Male ears, when grouped together, had significantly longer delays (8%) to the 0.78-kHz place in comparison to female ears. The effect of DPE stimulus level on delay is presented for stimulus levels between 15 and 60 dB SPL. These data support the use of DPE phase responses as estimates of cochlear traveling wave delay. In comparison with electrophysiological and psychophysical techniques this method is purely cochlear-based and has the advantage of being rapid and noninvasive.
A second cochlear-frequency map that correlates distortion product and neural tuning measurements
Authors: Allen J. B. , Fahey P. F.
Published: October 2005

Acoustic intermodulation distortion products (DPs) are generated by the nonlinear motion of the basilar membrane (BM) in the cochlea, and propagate back to the ear canal where they may be measured. One common method of measuring these distortion products is to hold the higher-primary frequency f2 fixed while varying the lower-primary frequency f1. When doing this, it is well known that the ear canal distortion product is maximum for a particular value of f2/f1, usually between 1.1 and 1.4. In fact all odd order distortion products of the form fd(n)=f1−n(f2−f1), n=1,2,3,... are maximum at the same fd(n), independent of the order n, but dependent on f2 which determines the place of DP generation. In this paper, it is argued that this maximum must result from filtering by micromechanical resonances within the cochlea. In fact the frequency where the neural tuning curve ‘‘tip’’ meets the ‘‘tail’’ is the same as the frequency where the distortion products are maximum. This suggests that each section of the basilar membrane must consist of two resonant impedances. The first is the usual series basilar membrane resonant impedance that gives rise to the characteristic frequency (CF). The second resonant impedance must be tuned to a frequency that is lower than the CF and must act as a shunt across the inner hair-cells, since it acts to reduce the forward transmission to the neuron, while, at the same time, it maximally couples all the distortion products back into the cochlear fluids, giving them a frequency dependent increase at its resonant frequency. Thus the proposed second mechanical resonance concept explains a great deal of complicated and confusing data. For pure tone excitation, the second resonance modifies the traveling wave excitation pattern (EP) basal to its characteristic place (CP). A good candidate for this second mechanical resonance would be a resonance of the tectorial membrane (TM), tuned to the neural tip-tail frequency at each place.
Unaliased discrete-time ambiguity function
Authors: Bekir Esmat
Published: October 2005

This paper presents a new analytical closed-form definition of the unaliased discrete-time ambiguity function. The new definition uses only the Nyquist rate and the same number of sampling points that would otherwise give an aliased spectrum with the existing definition. The discrete-time ambiguity function possesses properties and symmetry features that resemble those of the continuous-time counterpart. This paper also shows that the discrete-time ambiguity function possesses temporal and spectral correlation functions that are similar to and play the same role as those of the continuous-time counterparts. The new definition of the discrete-time ambiguity function is shown to be dual to that of the unaliased discrete time Wigner distribution given recently by the author [J. Acoust. Soc. Am. 93, 363–371 (1993)]. Specifically, it preserves all the continuous-time Fourier transform relations. Computer simulations are performed to validate the unaliasing property of the new definition.
An analytic model for the free in-plane vibration of beams of variable curvature and depth
Authors: Charpie James P. , Burroughs Courtney B.
Published: October 2005

In this study a flexible and powerful model is presented for the in-plane vibration of a beam whose curvature and depth are arbitrary, constrained only to such smoothness as can be accommodated by a quartic polynomial in the centerline arc length. The model includes the effects of shear deformation, rotary inertia, and centerline extensibility. The equations of motion are solved by an extension of the classic Galerkin method wherein the effect of boundary residuals is included. Timoshenko models are compared to other theoretical models and to experimental results; the comparisons are done for a variety of support schemes. A detailed study of a cantilever beam of variable curvature and depth is done and, finally, the utility and flexibility of the model is demonstrated for an arch whose shape is given only by a scale drawing, devoid of any other information except material properties.
Attenuation measurements of ultrasound in a kaolin–water slurry: A linear dependence upon frequency
Authors: Greenwood Margaret Stautberg , Mai Josef L. , Good Morris S.
Published: October 2005

The attenuation of ultrasound through a kaolin–water slurry was measured for frequencies ranging from 0.5 to 3.0 MHz. The maximum concentration of the slurry was for a weight percentage of 44% (or a volume fraction of 0.24). The goal of these measurements was to assess the feasibility of using ultrasonic attenuation to determine the concentration of a slurry of known composition. The measurements were obtained by consecutively adding kaolin to the slurry and measuring the attenuation at each concentration. After reaching a maximum concentration a dilution technique was used, in which an amount of slurry was removed and water was added, to obtain the attenuation as a function of the concentration. The dilution technique was the more effective method to obtain calibration data. These measurements were carried out using two transducers, having a center frequency of 2.25 MHz, separated by 0.1016 m (4.0 in.). The maximum attenuation measured in these experiments was about 100 Np/m, but the experimental apparatus has the capability of measuring a larger attenuation if the distance between the two transducers is decreased. For a given frequency, the data show that ln V/V0 depends linearly upon the volume fraction (V is the received voltage for the slurry and V0 is that obtained for water). This indicated that each particle acts independently in attenuating ultrasound. The data showed that the attenuation is proportional to the frequency and to the volume fraction. The results demonstrated the feasibility of using attenuation measurements to determine slurry concentration. Several theoretical models are discussed that describe the attenuation of ultrasound. The data obtained by several other researchers also show a linear dependence of attenuation upon frequency.
Photoacoustic waves generated by absorption of laser radiation in optically thin cylinders
Authors: Khan M. I. , Sun T. , Diebold G. J.
Published: October 2005

The properties of photoacoustic waves radiated by an optically thin, infinitely long fluid cylinder can be found through solution of the wave equation for pressure. The amplitude and phase of the acoustic wave emitted by a cylinder irradiated by sinusoidally modulated light are first determined. The response of the cylinder to a pulse of radiation whose duration is short compared with the transit time of sound across the cylinder is then found by Fourier transformation of the frequency domain solution. The expressions derived here for the photoacoustic pressure are shown to give the radial eigenfrequencies of the cylinder, the frequency of oscillation of a cylindrical bubble, and a response of the cylinder to long light pulses proportional to the 1/2th time derivative of the optical pulse. The character of the photoacoustic waves is shown to be determined, in part, by repeated reflections of the outgoing cylindrical wave at the interface between the cylinder and its surrounding fluid. The results of several experiments with pulsed laser excitation of fluid cylinders are reported.
Simultaneous acoustic emission and ultrasonic tomographic imaging in anisotropic polymer composite material
Authors: Chow T. M. , Hutchins D. A. , Mottram J. T.
Published: October 2005

This paper describes experiments in which acoustic emission and ultrasonic tomography were performed concurrently on samples of anisotropic glass fiber reinforced polymer composite in a direct tensile test. Propagating cracks were monitored by acoustic emission throughout the loading phase, and the material imaged using ultrasonic tomography at regular intervals. Analysis of the data indicated that propagation of the main crack was controlled by the breakage of the continuous glass fibers. The region of microfracture damage seemed to extend well beyond the visible crack. The technique has promise for the study of changes in acoustic properties of materials under applied stress.