bluuebunny/crossref_metadata_2025 huggingface dataset:
Joint detection-recognition of amplitude modulation
Authors: Sheft Stanley , Yost William A.
Published: July 2002

Joint detection-recognition ability was measured for amplitude modulation. On each trial there were two subject responses, one for detection and the other for recognition. Stimuli were samples of wideband noise sinusoidally modulated at either 4, 16, 64, or 256 Hz. Conditions included all pairwise combinations of the four AM rates. Rate uncertainty led to only a slight decrement in detection ability with little effect of the extent of the separation between the two rates. Recognition performance was always poorer than detection ability with recognition near chance on trials in which the detection response was incorrect. When one of the AM rates was 4 Hz, the detection-recognition theorem [Starr et al., Radiology 116, 533–538 (1975)] provided a reasonable prediction of recognition ability. For the three other pairwise combinations of AM rate, recognition performance was poorer with the theorem failing to account for the extent of the decrement. The theorem requires orthogonality of signals. Results then suggest independence of 4 Hz versus higher rate processing, and also correlation in processing the higher rates. This pattern of orthogonality is consistent with two rate-dependent cues in modulation processing. [Work supported by NIH.]
Attention and the build-up of auditory stream segregation
Authors: Carlyon Robert P. , Cusack Rhodri , Foxton Jessica M. , Robertson Ian H.
Published: July 2002

In the baseline condition of experiment 1, subjects were presented with a repeating ABA–ABA sequence of 125-ms tones in their left ear, and indicated, throughout the entire 20-s sequence, whether they heard one or two streams. The proportion of ‘‘two stream’’ responses increased during the course of each sequence. This build-up of stream segregation was greatly reduced when, for the first 10 s of each sequence, subjects performed a competing task on a train of noise bursts presented to the right ear. The competing task involved identifying the amplitude envelope of each noise burst as either rising or falling. The noise bursts had no effect in a third condition, in which subjects were instructed to ignore them. Experiment 2 showed that a substantial build-up of streaming can still be observed when subjects switch tasks halfway through the tone sequence, provided that both tasks require them to continually attend to the tones. We conclude that attention is crucial for the build-up of stream segregation, and that our results are inconsistent with models of streaming based purely on peripheral, ‘‘automatic’’ neural mechanisms.
Structural-acoustic analysis of 3-D curved shell with a discontinuity using analytical/numerical matching (ANM)
Authors: Park Christopher , Franzoni Linda , Bliss Donald
Published: July 2002

Analytical/numerical matching (ANM) is used to determine the structural vibration of a curved shell driven at a single support. The ANM solution decomposes the problem into global, local, and matching subproblems. The global problem addresses large-scale effects with structural discontinuities replaced by smooth distributed forces. The local problem models the rapidly changing region around a structural discontinuity. These constituent problems are solved independently by the most efficient method available. Here, the local problem is solved numerically using 3-D solid finite element analysis (FEA) and the matching problem is solved analytically, using the Love–Timoshenko shell equations. The global problem is decomposed modally in azimuth, leaving a corresponding FEA problem in the axial direction for each mode. Due to the smoothness of the global problem, relatively few modes are required for the modal decomposition and the affiliated FEA problem can be solved using a low resolution. An advantage of the ANM method is its ability to capture the detailed response of structures with geometric complexities without having to incorporate the complexity (via higher-order elements or high mesh densities) in the modeling of the large global problem. [Work sponsored by ONR.]
Sound transmission through finite laminated composite panels using statistical energy analysis
Authors: Patil Avinash R. , Crocker Malcolm J.
Published: July 2002

Laminated composite panels are widely used in aerospace structures and other applications where weight reduction of the structure is desired without compromising the strength. They can be made up of a number of layers of unidirectional laminas. Sound radiation and sound transmission properties of these panels are different than those for isotropic panels. This is because of the variation of the material properties along the direction of bending wave propagation. During this work, analysis of those finite laminated composite panels which exhibit uncoupling of bending/twisting phenomenon is done. A bending wave number diagram is drawn to study the variation of bending wave number with respect to the angle of bending wave propagation for a given frequency. Instead of a single critical frequency as in the case of an isotropic panel, a band of critical frequencies is observed. In this band of critical frequencies, coincidence occurs only at a certain angle of bending wave propagation for a particular frequency. Frequency average radiation efficiency of such a panel is predicted by considering the variation of wave number along different directions of bending wave propagation. Modal density is predicted from the bending wave number diagram. Transmission loss of the panel is predicted using the statistical energy method.
Le Chatelier’s Principle in noise control
Authors: Maidanik G.
Published: July 2002

Le Chatelier’s Principle is perhaps better known to those who studied chemistry at the university. Therefore, I find that few in the noise control community are familiar with this principle. This paper features some examples of noise control problems in which ‘‘the Principle’’ plays a role. For noise control purposes and for the record, Le Chatelier’s Principle states that ‘‘when a dynamic system is modified with the intention of achieving a high degree of change in the noise issued by this dynamic system, the achievement is mitigated by the implementation of the modification.’’
Music-masked maximal-length sequences for auditorium acoustic measurements
Authors: Xiang Ning , Sabatier Charles
Published: July 2002

Maximal-length sequence (M-sequence) measurement technology has gained acceptance within the architectural acoustics community for quite some years. Owing to the high noise immunity and computational efficiency of the fast M-sequence transform, acoustic qualities in auditoria can be determined quickly and with satisfactory precision. The present work investigates the use of music signals to mask M-sequence excitations. The inherent cross-correlation mechanism of the fast M-sequence transform makes it possible to determine room impulse responses with a positive music/M-sequence ratio (expressed in dB). The feasibility, limitations, and potential applications for using music-masked M-sequences in taking auditorium impulse responses measurements will be discussed in the presentation.
Insight into the diagnosis of conductive hearing loss using wideband acoustic reflectance measurements of surgically modified human temporal bones
Authors: Miller Antonio
Published: July 2002

There is mounting evidence to suggest that wideband acoustic impedance/reflectance measurements will aid in the clinical diagnosis of various middle ear pathologies. In preparation for clinical trials, wideband pressure reflectance measurements (100 Hz to 8 kHz) were made looking into the ear canals of three human temporal bones which were surgically modified to simulate five possible pathological conditions [unpublished data of J. Allen, G. Ball, S. Nishihara, and R. Goode]. The experimental procedure, data, and analysis are presented for the different modifications. The unmodified, air-filled tympanic cavity data characterize the baseline losses for the entire system. A fluid-filled typanic cavity characterizes the effect of fluid loading on the tympanic membrane, simulating the condition of acute and chronic otitis media (middle ear infection). The fixed stapes condition simulates the effect of otosclerosis (calcification of the stapes footplate). Disarticulated stapes and the severed stapedius tendon conditions are both symptoms associated with chronic otitis media or cholesteatoma (middle ear cysts). Finally, the fixed malleus condition can be a warning sign of otitis media, but can easily be misdiagnosed as otosclerosis. It is hoped that this work will provide a physical basis for the interpretation of wideband pressure reflectance data collected in future clinical trials.
Glottal pressure profiles for a diameter of 0.04 cm
Authors: Scherer Ronald C. , Shinwari Daoud
Published: July 2002

Computer models of phonation often rely on aerodynamic equations for flow through the glottis. Usually the aerodynamic equations have come from empirical work with steady-flow models made from hard material. The equations simplify the pressure-flow-geometry relations through the larynx. The model used here (model M5) has 14 pressure taps on the vocal folds to give rather complete pressure profiles. Pressure profiles will be reported for symmetric glottal shapes, a minimal diameter of 0.04 cm, and nine glottal angles (uniform; convergent, and divergent 5, 10, 20, and 40 deg) for transglottal pressures of 3, 5, 10, and 15 cm H2O. The glottis is rectangular in the anterior–posterior direction, with a glottal length of 1.2 cm. Results indicated that the pressure coefficient for the glottal entrance ranged from 1.09 to 1.60 with an average of 1.33 (compared to van den Berg’s 1.375). The value decreased as flow increased for any specific glottal angle. The transglottal pressure coefficient ranged from 1.00 to 1.82 with an average of 1.28. The average value for the uniform glottis was 1.63. Values decreased as flow increased. Pressure profiles will be compared to predictions from current glottal aerodynamic equations. [Work supported by NIH Grant 1R01DC03577.]
Nonlinear surface waves in isotropic elastic substrates with thin films
Authors: Ohm Won-Suk , Hamilton Mark F.
Published: July 2002

Surface waves in isotropic elastic solids are nondispersive. Considered here is the effect of dispersion, due to a thin solid film on the surface of an isotropic substrate, on nonlinear propagation. The analysis is performed with the theoretical model developed by Zabolotskaya [J. Acoust. Soc. Am. 91, 2569 (1992)] augmented to include dispersion. The dispersion relation is obtained from linear theory but is otherwise exact. Approximations leading to a relation of the Korteweg–de Vries or Benjamin–Ono type, sometimes proposed for the study of dispersive nonlinear surface waves, are not employed. Both loading and stiffening films are considered. Loading films decrease the surface wave speed. Stiffening films increase the surface wave speed until it equals the shear wave speed in the substrate, where cutoff of the surface wave mode occurs. Computations were performed with elastic moduli for a fused quartz substrate, which exhibits negative nonlinearity in the sense that rarefaction rather than compression shocks form in the horizontal particle velocity waveform. Gold (loading) and alumina (stiffening) films are considered. Weak, moderate, and strong dispersion (corresponding to increasing film thickness) relative to nonlinearity are examined. Stationary wave solutions are obtained for the alumina film. [Work supported by ONR.]
New techniques to reduce observer inconsistency in psychoacoustic experiments
Authors: Lapsley Miller Judi A.
Published: July 2002

One of the biggest problems still facing experimental psychophysics is observer inconsistency. Observer inconsistency degrades performance, hampering comparisons with other observers and theoretical predictions. By repeating an experiment multiple times, using the same stimuli, observer inconsistency can be reduced and asymptotic errorless performance estimated by using group operating characteristic (GOC) analysis and function of replications combined estimation (FORCE) analysis, respectively. These new techniques are described and illustrated with results from various psychoacoustic experiments, showing that humans are sometimes capable of performing as well as an ideal observer once observer inconsistency is reduced.
Detection advantage with coherent amplitude modulation for speech filtered into narrow bands
Authors: Hall Joseph W. , Buss Emily , Grose John H.
Published: July 2002

Introduction of masker amplitude modulation can improve detection thresholds for a masked signal in a number of masking paradigms. In some cases this detection advantage depends on the coherence of modulation across a relatively wide range of frequencies. In the current experiment 43 spondees were recorded from a single male talker and employed as the signal in a forced choice, closed set word identification task. Both the spondee signal and the speech-shaped Gaussian noise masker were filtered into six narrow bands. Either the signal or the masker was amplitude modulated by an 8-Hz raised cosine, and that modulation was either coherent or random across bands. Thresholds were consistently lower when the masker was modulated with coherent rather than random patterns of AM. No difference between coherent and random AM was observed when the speech signal was modulated. This finding suggests that the advantage observed with coherent masker AM may not have been driven simply by the coincidence of speech energy across frequency appearing in masker ‘‘dips.’’ Other explanations will be discussed, including a possible interpretation in terms of comodulation masking release.
Representational specificity of lexical form in the perception of spoken words
Authors: McLennan Conor T. , Luce Paul A. , Charles-Luce Jan
Published: July 2002

Exemplar and traditional abstractionist models of lexical representation were evaluated by examining flapping in American-English. According to abstractionist models, flaps are considered neutralized surface realizations of the underlying phonemic forms /t/ and /d/, with fully specified /t/ and /d/ forms of words represented in memory. Exemplar models, on the other hand, assume flapped tokens of spoken words have full representational status. An investigation of the representation of flaps in American-English was conducted using the repetition priming paradigm. Participants shadowed spoken words in two blocks of trials. Stimuli in the first block were primes and those in the second block targets. Primes and targets consisted of flapped and carefully articulated bisyllabic words. Time to shadow target words in the second block was measured as a function of prime type. The shadowing time results provide evidence for underlying abstract representations. The implications of these results for the theories of form-based lexical representations will be discussed.
Multiple scattering effects produced by a cylindrical shell in shallow water
Authors: Sarkissian Angie
Published: July 2002

Multiple scattering effects produced by a finite ribbed cylindrical shell placed in a shallow-water environment are evaluated for the monostatic geometry. A combination of finite elements/infinite elements methods and the method of superposition is applied to compute first-order multiple scattering effects produced by a cylinder placed close to the shallow-water surface. Results are shown for a cylinder having a length to a diameter ratio of 6.8 at a ka=10, where k is the wave number in the fluid at the location of the cylinder and a is the radius of the cylinder. [Work supported by ONR.]
Sediment roughness estimation with ROV mounted lasers
Authors: Chotiros Nichoas P. , Piper James N. , Ward Brian S. , Smith D. Eric , Gage David C. , Banks Roger A. , Smith David L.
Published: July 2002

A simple method of measuring underwater sediment surface roughness was tested over a sandy sediment off the west coast of Florida, as part of the Sediment Acoustics Experiment (SAX99). The process was integrated into an acoustic data acquisition system, and allowed roughness measurements of the seafloor without interference with the acoustic data acquisition process. The method employed lasers mounted on a remotely operated vehicle (ROV). Each laser was a red He–Ne class IIIa with output power less than 5 mW. A cylindrical lens was used to spread the laser beam into fan, which was directed downward to produce a stripe on the sediment. Viewing from an oblique angle, the profile of the sediment directly under the stripe is obtained. The information was recorded on videotape, digitized, and processed to obtain roughness statistics. [Work supported by ONR, Ocean Acoustics.]
Analysis of sound waves in a sandy sediment by focused array
Authors: Chotiros Nichoas P. , Smith D. Eric , Piper James N. , McCurley Brett K. , Gage David C. , Ma Harvey
Published: July 2002

The objective was to determine the underlying physical processes in the penetration of sound into sandy ocean sediments, particularly at shallow grazing angles. Signals were collected from a buried acoustic receiving array in a sandy sediment off the west coast of Florida, as part of the Sediment Acoustics Experiment (SAX99). The array was insonified by a wideband sound source carried on a remotely operated vehicle (ROV). The discrimination between refraction and scattering processes was of particular interest. To this end, an array-processing method was used that employed focusing to distinguish between refracted signals from a distant source and scattered signals from scatterers in the near field of the array. Sound waves entering the sediment at steep angles were clearly refracted. In the case of shallow grazing angles, the results were much more complicated. [Work supported by ONR, Ocean Acoustics.]
Practical approaches for utilizing the plane-wave reflection coefficient as input data for inferring geoacoustic properties of the seabed
Authors: Souza Luiz L. , Becker Kyle M. , Frisk George V.
Published: July 2002

Exact inverse techniques for inferring seabed geoacoustic properties typically require measurements of the plane-wave reflection coefficient as input data. Specifically, assuming the same constant density throughout the water column and the seabed, the reflection coefficient as a function of incident angle at a fixed frequency can be used to obtain a unique estimate of the sound-velocity profile in the bottom. In this paper, practical issues associated with implementing techniques such as the Gelfand–Levitan method in the deep and shallow ocean are discussed. These include the estimation of the reflection coefficient from point-source measurements using the Hankel transform, and the incorporation of a known density discontinuity at the water–bottom interface into the inversion scheme. Examples based on realistic seabed environments are presented. [Work supported by ONR.]
Characterization of bone using longitudinal and shear wave imaging techniques
Authors: Wu Junru , Ye Shigong , Peach John
Published: July 2002

Recently a computer-controlled scanning ultrasound imaging system was developed in our laboratory. It includes a pair of broadband 48-MHz focusing copolymer transducers. The apertures of the transducers and their f-numbers were identically equal to 2 mm and 2.25, respectively. A specimen can be moved in a 10-μm increment in its plane and its normal direction can be rotated along the ultrasound propagation direction. It can be used to produce transmission-mode shear-wave as well as longitudinal-wave images of solid specimens. Shear waves in solids were generated by mode conversion. The results of the longitudinal and shear-wave ultrasound images for a piece of compact bovine bone obtained using this system are presented. Shear-wave images combined with longitudinal images can provide a complete evaluation of elastic moduli of bone.
In vitro study of mechanisms of transient response imaging
Authors: Kim Suor , Everbach E. Carr
Published: July 2002

Transient response imaging (TRI), or intermittent imaging, has been shown to produce increased myocardial contrast when fluorocarbon-filled microbubble contrast agents are used to visualize the heart. By lowering the frame rate from around 40 Hz to below 1 Hz, it has been hypothesized that less microbubble destruction occurs via inertial cavitation [E. C. Everbach, Shouping Li, and Thomas R. Porter, J. Acoust. Soc. Am. 102, 3154 (1997)]. To test this hypothesis in vitro, a flow-through system of diluted PESDA contrast agent in distilled water was insonified at 1 MHz using 10, 100, and 1000 microsecond pulses at PRFs of 0.5, 1.0, 10, and 30 Hz. Inertial cavitation was quantified by a narrow-band 20-MHz passive transducer placed confocally with the 1-MHz insonifying transducer. Results and relevance to in vivo experiments will be discussed.
Radiation impedance of a finite circular piston vibrating normal to an isotropic viscoelastic half-space with application to medical diagnosis
Authors: Zhang Xiangling , Royston Thomas J. , Mansy Hussein A. , Sandler Richard H.
Published: July 2002

In a recent study [J. Acoust. Soc. Am. 106, 3678–3686 (1999)], a new analytical solution was developed and validated experimentally for the problem of surface wave generation on a linear viscoelastic half-space by a rigid circular disk located on the surface and oscillating normal to it. The results of that study suggested that, for the low audible frequency range, some previously reported values of shear viscosity for soft biological tissues may be inaccurate. Those values were determined by matching radiation impedance measurements with theoretical calculations reported previously [J. Acoust. Soc. Am. 23, 707–714 (1951)]. In the current study, the new derivation is extended to the calculation of radiation impedance. Comparisons are made with prior theory and experiments to determine which theory is more accurate and what range of values for shear viscosity is more accurate. Measurement of skin surface radiation impedance has been studied by a few researchers for rapid, nonintrusive diagnosis of a variety of specific medical ailments. It is hoped that the developments reported here will advance these techniques and also provide insight into related diagnostic methods, such as sonoelastic imaging and other methodologies that utilize disease-related variations in soft tissue viscoelastic properties. [Work supported by a grant from the Whitaker Foundation.]
A new analytic model of piezoelectric stack actuators including ferroelectric nonlinearities
Authors: Pasco Yann , Berry Alain
Published: July 2002

The proposed numerical modeling of piezoelectric phenomena combines a mathematical model of hysteresis and a macroscopic theory of ferroelectricity including the nonlinear effect of polarized ceramics. Most of the time, modeling is sought between applied electric field versus displacement. Such an analytic model does not take into account ferroelectric phenomena and as a consequence never gives information about ferroelectric characteristics of ceramics, but gives a simple model of the ceramics’ behavior. Another advantage of the new model is that it can still be accurate even if the ceramic is blocked in force. In order to simplify equations, the quasistationarity of electric field is assumed and three-dimensional equations will be reduced to a one-dimensional stack actuator. Such a model could be used in active control of vibrations.
Experimental results of localized wave experiments
Authors: Lewis D. Kent
Published: July 2002

The theory for several low diffraction beams has been upheld by experimental verification in several tests to date. Both the modified pulse spectrum and the superposed Gaussian beams have been verified by Livermore projects in the laboratory and in open water tests. Test methods, instrumentation, data analysis techniques, and results will be discussed in this presentation. [This work was performed under the auspices of the Department of Energy by Lawrence Livermore National Laboratory under Contract W-7405-ENG-48.]
Performance prediction of localized waves using a simulator
Authors: Chambers David
Published: July 2002

Numerical simulations of the performance of localized waves have proved useful in planning experiments and doing parameter studies. In this talk predictions of axial energy decay and far-field spot patterns for the modified pulse spectrum and superposed Gaussian pulses are investigated as a function of their input parameters. These predictions are confirmed by recent experimental data and comparisons with conventional tone bursts are shown. Comparisons are also made with analytical predictions for near-field transition distance and far-field radiation patterns.
Developing noise–dosage weighting functions for animals
Authors: Bowles Ann E. , Pater Larry
Published: July 2002

Human A- and C-weighting functions have been used to calculate noise dosage estimators in studies of wild birds and mammals. It would be better to develop functions specifically designed for them, perhaps taking into account psychophysical differences taxon by taxon. Unfortunately, methods that yield human weighting functions cannot be generalized to most animals. First, human weighting functions are based on equal-loudness contours, but these cannot be measured directly in wild animals. Possible alternate weighting functions include (1) the auditory threshold function of the species/taxon, standardized to 0; (2) the auditory threshold function shifted by a scalar quantity to reflect varying sensitivity; and (3) equal-latency functions, which fit equal-loudness curves well in humans. Second, it is not clear that such weighting functions yield efficient predictors of effect. While human A-weighting is used to calculate noise dosage in studies of both nonauditory and auditory effects, a single weighting function need not yield the best dosage estimator for effects in other animals. In studies of impact on behavior, equal-response-threshold functions (frequency-specific thresholds for behaviors) may be more efficient. Such alternative measures must be compared empirically before dosage estimators can be standardized.
Enhanced release of drugs from a novel polymeric film coated with self-healing, ordered methylene chains induced by hydrodynamic shear
Authors: Porter Tyrone M. , Mourad Pierre , Crum Lawrence A. , Kwok Connie S. , Ratner B. D.
Published: July 2002

The effect of numerous stimuli upon the release of drugs and other molecules from polymeric substrates has been of great interest in the drug delivery community. Ultrasound has proven to be an effective stimulus for the controlled release of drugs from polymer films. However, the mechanism by which this controlled response occurs has yet to be fully understood. In this study, the ability of shear forces generated by microstreaming around a single ultrasonically stimulated bubble to reversibly increase the release of the drugs from a coated polymer film is demonstrated. The polymer film is loaded with the drug ciprofloxacin and then coated with methylene chains consisting of 12 hydrocarbon chains. The leaching rate of the drug thus depends upon the extent of surface coverage by the methylene chains. A single oscillating bubble in a fluid medium has the capacity to drive streaming at the surface of the polymer film and disrupt the methylene chain coating. An increase of drug concentration in suspension as high as ten times the baseline and controls was achieved, which implies an increase in the leaching rate. After treatment, the leaching rate returns to baseline levels, suggesting the methylene chains reorganize upon the polymer surface.
Acoustic mechanisms as an enhancer for transdermal drug delivery
Authors: Park E. J. , Jung K. I. , Yoon S. W.
Published: July 2002

An acoustic enhancer for transdermal drug delivery has been studied for several decades in the field of engineering. However, its delivery mechanisms are not well understood. In this study, simple experiments were proposed to simulate a human skin system with a rat back skin for transdermal insulin delivery. Unfocused 0.5-, 1-, and 3-MHz ultrasound transducers were used for acoustic enhancers, and a heating wire loop was used for a nonacoustic enhancer. Ultrasound worked as a very effective delivery enhancer. The acoustic enhancer even gave better enhancement of insulin transportation than the nonacoustic enhancer, such as the heating wire loop, while almost the same amount of heating from both enhancers was applied to the diffusion cell. These results show that the thermal effect in the acoustic enhancer works as a major mechanism for transdermal insulin delivery. However, the nonthermal effects of ultrasound was also observed to contribute to enhance the transdermal insulin delivery.
Primary microphone calibration has become an easy task
Authors: Frederiksen Erling
Published: July 2002

New automated calibration equipment and software have made the quite complex pressure reciprocity calibration of microphones an easy and very accurate method. Today, the method can be applied not only by the specialists of National Calibration Laboratories but also by technicians of other laboratories. Since its invention in 1940, the method has become highly refined and is now used for essentially all primary calibrations. Many physical, electrical, and mechanical parameters of relatively small importance are now taken into account by the present international standard IEC61094-2 and by the software of the new equipment. Therefore, the system works with a high accuracy, better than ±0.03 dB in the best range. As all measurements and calculations are automated, this is obtained together with a short calibration time and a simple operation. Another improvement is due the applied plane wave couplers, which can be used up to high frequencies (10 kHz with 1-in. and 25 kHz with 1/2-in. microphones) without the hydrogen filling required by the large-volume couplers, which were commonly used in the past. This eases the calibrations significantly and eliminates safety problems. System features and calibration results will be discussed.
Dynamic sound localization using spatial awareness networks
Authors: Aarabi Parham
Published: July 2002

This paper proposes a sound localization algorithm that utilizes spatial awareness networks (SAN). SANs are an integrated network consisting of a probabilistic location inference model along with an adaptive observability network. This structure yields a synergic mechanism in which individual sensors are configured independently. This leads to a sound localization system that has no limitations on the number, orientation, or position of the microphones.
The direct and inverse problems in 3D modeling of horns: Current results and future directions
Authors: Amir Noam , Kemp Jonathan
Published: July 2002

Modeling of acoustic horns is a subject that has been studied extensively for at least a century. It is only with the advent of the digital computer that it has become feasible to study the coupling between the various transversal modes in such horns. In this paper we examine the influence of the higher-order modes, obtained through a numerical solution. We show that though they may influence the acoustic field considerably, their influence on the input impedance is much smaller. We demonstrate that for many horns, taking only one higher-order mode into account improves accuracy to a great extent. We also show how the higher-order modes can influence parameters used in the plane wave model, such as radiation impedance and the end correction. Preliminary results in solution of the inverse problem, taking higher-order modes into account, are also discussed. Current algorithms incorporate plane waves only, and thus are inaccurate at areas of large flare. Finally, we discuss the more practical sources of inaccuracy in measurements: the relationship between spatial and temporal discretization, and transformation of measurements and simulated results between frequency and time domains. We summarize with some philosophical musings on the meaning of ‘‘accuracy’’ when dealing with musical instruments.
Acoustic Faraday effect and transverse waves in a superfluid
Authors: Halperin William P. , Lee Yoonseok , Haard Thomas M. , Sauls James A.
Published: July 2002

Acoustic waves provide a powerful tool for studying the structure of matter. The speed, attenuation, and dispersion of acoustic waves give useful details of the molecular forces and microscopic mechanisms for absorption and scattering of acoustic energy. In solids, both compressional and shear waves occur, so-called longitudinal and transverse sound. However, normal liquids do not support shear forces and consequently transverse waves do not propagate in liquids with one notable exception, the quantum liquid phase of 3He. We have observed rotation of the polarization of transverse sound waves in superfluid 3He−B in a magnetic field. This magneto–acoustic effect is the direct analog to the magneto–optical effect discovered by Michael Faraday in 1845, where the polarization of an electromagnetic wave is rotated by a magnetic field along the propagation direction. Our experiment [Nature 400, 431 (1999)], is the first demonstration of the existence of propagating shear waves in a liquid.
The existence of internal acoustic radiation modes in a cylindrial acoustic cavity
Authors: Johnson Wayne M.
Published: July 2002

The external acoustic radiation operator maps a boundary-valued quantity, such as the normal surface velocity of a radiator, to the pressure radiated into the field. It has been shown that the decomposition of the acoustic radiation operator results in a set of orthogonal singular velocity patterns or acoustic radiation modes. It has also been demonstrated that superposition of selected acoustic radiation modes can be used to prescribe surface velocity distributions resulting in poor radiation of pressure into the field. The development of acoustic radiation modes for the interior cavity problem may provide insight into the physics of structural acoustic coupling between, for example, a thin cylindrical shell and the enclosed acoustic volume. However, the existence of these radiation modes for the interior problem is uncertain. Also, if these interior radiation modes do exist, do they in fact coincide with the acoustic cavity or normal modes? This study intends to explore the existence of acoustic radiation modes for the interior cavity problem and their relationship to the cavity modes of a right circular cylindrical acoustic volume of air.
A combined experimental/FEM model for predicting vehicle panel acoustic noise contribution
Authors: Lim Teik
Published: July 2002

Radiated acoustic noise contributions from the structural panels that form the inner shell of the vehicle body to the interior sound pressure response are modeled using an approximate spectral formulation. The approach essentially utilizes the theoretical interior acoustic sensitivity terms derived from a finite element model and measured spatial-averaged structural-acoustic spectra. The finite element calculation is validated by comparison to a set of experimental acoustic transfer functions. In addition, an experimental setup for measurement of the sound intensity and structural-acoustic response is used to acquire the cross and auto power spectra needed to predict the relative mean-squared velocity term of each control plane near the panel surface. These velocity functions are then combined with the acoustic sensitivity terms to compute the individual panel contribution function. The proposed approach is applied to a specific case of a passenger car to compute the acoustic noise spectra in 1/12 octave band form at selected positions in the passenger compartment. The calculations show excellent match with the overall experimental results. Also through this example, the approximate computational scheme is proven to be generally quite robust and effective for analyzing higher frequency interior noise problems.
Combined Helmholtz equation–least squares (CHELS) method for reconstructing radiated acoustic pressure fields
Authors: Wu Sean , Zhao Xiang
Published: July 2002

A combined Helmholtz equation–least squares (CHELS) method is developed for reconstructing acoustic pressures radiated from an arbitrary object. This method combines the HELS method [Wang and Wu, J. Acoust. Soc. Am. 102, 2020–2032 (1997); Wu and Yu, ibid. 104, 2054–2060 (1998)] and boundary element method (BEM)-based Helmholtz integral formulation. The main advantage of the HELS method is its simplicity in expressing the radiated acoustic pressure in terms of an expansion of orthonormal basis functions. However, the accuracy of reconstruction may deteriorate with the increase of complexity of source geometry. This is because the convergence of the basis functions becomes poorer for an irregular surface than for a smooth surface. The BEM-based integral formulation allows for reconstruction of the radiated acoustic pressures on an arbitrarily shaped object. However, the number of measurements required for reconstruction is often too large to make the process practical. In the CHELS method, only a finite number of measurements are taken to establish the HELS method. Once this is done, enough field pressures are generated using the HELS method, which are then taken as input to the BEM-based integral formulation to reconstruct acoustic pressures everywhere. [Work supported by NSF Grant No. CMS-9802847.]
The intraspeaker variability of pitch in Mandarin and English subjects producing disyllabic words
Authors: Nissen Shawn , Gibbons Christopher
Published: July 2002

Considering their use of pitch to convey lexical information, do tone language speakers develop greater control over pitch mechanisms, thus exhibiting less overall pitch variability than speakers of intonation languages? One previous researcher has argued that tone language speakers exhibit a ‘‘remarkably stable and precise absolute pitch template’’ when reading word lists [Deutsch et al., J. Acoust. Soc. Am. 106, 2267 (1999)]. The present study aims to investigate the intraspeaker pitch variability of Mandarin and English speakers when producing disyllabic words. Specifically, this research will examine (1) intraspeaker pitch variability between Mandarin and English speakers, (2) the degree of pitch stability exhibited by speakers of both languages, and (3) the effects of elicitation condition on a speaker’s pitch variability. Subjects will produce initially stressed, disyllabic words (similar segmental structure) in their native language elicited through picture identification. Randomized blocks containing similar target items will be presented under two elicitation conditions. To measure possible ‘‘list effects’’ the second elicitation condition will contain an intervening masking task. Measures of fundamental frequency change of target nuclei will be obtained at four locations: start point, end point, high point, and low point. A three-way ANOVA will be used to analyze the pitch variability data.
Quantitative three-dimensional imaging with diffracting wavefields
Authors: Devaney Anthony J.
Published: July 2002

The general theory of quantitative imaging of three-dimensional, semi-transparent (weakly scattering) objects using scalar waves is presented. The theory is developed for the case of transmission type experiments appropriate to ultrasound diffraction tomography but is applicable with minor modifications to reflection geometries appropriate to pulse echo imaging. The imaging problem is formulated from first principles in terms of the three-dimensional scalar wave equation and is shown to reduce ultimately to an inverse scattering problem. By use of certain linearizing approximations the inverse problem is shown to reduce to a conventional (coherent) imaging problem having a well-defined point spread function (PSF) that can be computed in terms of the experimental parameters and imaging geometry. It is shown that this formulation allows quantitative three-dimensional imaging to be treated completely analogously to coherent optical imaging and, in particular, leads to a characterization of image quality in terms of the PSF and its spatial Fourier transform, the coherent transfer function (CTF). Inherent limitations of three-dimensional imaging are discussed based on the computed PSF for certain canonical geometries. These limitations are shown to be partially overcome by using suites of scattering experiments and/or beam scanning techniques such as focus-on-transmit and focus-on-receive. The talk includes a discussion of the validity of the weak scattering approximations that underlie the imaging model as well as a discussion of the use of the wave aberration function for characterizing image quality. The talk is illustrated with simulated and experimental results.
Computing resolution in acoustic tomography
Authors: Berryman James G.
Published: July 2002

The resolution of images obtained using acoustic tomography is important both after the fact, as a means of evaluating the usefulness of the final image, and before the fact, when the measurement system of sources and receivers is being designed according to some preset criteria specified by the users. Resolution computations can actually be significantly more difficult and expensive than computing the image itself. Our purpose then is to show how resolution can be computed economically in almost all cases, and to provide a means of comparing the resolution characteristics of many of the common approximate inverse methods. Means of obtaining the effective resolution operator for such standard iterative inversion procedures as conjugate gradients, Lanczos, and LSQR are provided while avoiding the more common approach of producing a singular-value decomposition (SVD) of the operator being inverted. The methods discussed produce very easy-to-understand results for purposes of analysis, but require reorthogonalization of the Krylov vectors/operators produced by realistic iterative procedures in finite precision. Although the need for reorthogonalization increases the expense of the procedure somewhat, it still produces the desired results with much greater efficiency than could be obtained by computing an SVD of the full operator.
Analysis of time-reversing array performance for a broadband pulse propagation in the presence of ambient noise
Authors: Dowling David R. , Khosla Sunny R.
Published: July 2002

The properties of time-reversing arrays (TRAs) are being investigated for both active and passive underwater applications. Previous computational and experimental investigations have shown that automatic spatial and temporal pulse compression are possible with a TRA even when the acoustic environment is unknown. It has also been found that ambient or electronic noise limits the narrow-band performance of TRAs. In this presentation, the results from a computational study of the performance of a TRA that receives and transmits broadband pulses in a noisy environment will be shown. Pulsed-signal retrofocusing is simulated in noisy free-space and sound-channel environments via Monte Carlo techniques. The noise field is treated as white in the signal band and omnidirectional in space. The sound-channel simulations are done with a Fourier superposition of calculations from a parabolic equation code (ram by M.D. Collins). Theoretical scaling laws for the probability of a retrofocus occurring as the noise level increases are also presented. At the time and place of the retrofocus, results from both approaches suggest that pulse compression allows broadband TRAs to outperform narrow-band TRAs in noisy environments. [Work sponsored by ONR, Ocean Acoustics.]
Autocorrelation model for pitch processing in the frog’s auditory nerve
Authors: Simmons Andrea M.
Published: July 2002

Bullfrogs’ reactions to simulated vocalizations are sensitive to disruption of the 100-Hz 1st harmonic periodicity caused by the presence of inharmonic frequency components or changes in component phase. This behavioral preference for a specific range of periods indicates that representation of periodicity ‘‘pitch’’ may be the basis for evaluation of conspecific calls. Anuran auditory-nerve fibers phase-lock to the 1st and sometimes the 2nd or 3rd harmonic of multiple harmonic signals. Interval histograms of fiber responses reflect the complex pitch of both harmonic and inharmonic stimuli. We developed a pitch model that estimates pitch-period autocorrelation functions from all-order interval histograms across frequency channels by implementing model neurons designed to replicate the frog’s auditory nerve. Histograms are aligned in time across channels before being combined into a single pitch image (‘‘strobing’’ in the Patterson pulse-ribbon model; ‘‘dechirping’’ in bat sonar target-ranging). The resultant output yields a sharp pitchlike image, consistent with both behavioral and physiological results. Robust 1st-harmonic pitch images are produced for multiple harmonic signals, and even two-component sounds require only a few parallel fibers to yield a robust 1st-harmonic pitch.
Auditory temporal computation in fish
Authors: Crawford John
Published: July 2002

Fishes offer valuable opportunities for investigating auditory temporal computation. They use simple communication sounds. The ears and central auditory pathways are similar to those of other vertebrates, but the periphery is not specialized for frequency analysis as it is in mammals, and acoustic temporal analysis predominates. In the fish Pollimyrus, a small gas-filled bladder is coupled to each sacculus and translates acoustic pressure to motion of the hair cells. Behaviorally, these fish are sensitive to small differences in the temporal structure of sounds. Neurophysiological recordings from the auditory nerve show that sounds are faithfully encoded by the intervals between phase-locked spikes. This representation is transformed as it ascends the pathway, and is used in neural computations. In the auditory midbrain neurons are activated by particular temporal patterns. The selectivity of the auditory feature detectors results from neural computations that use synchronized trains of spikes as input. Computational modeling supports the hypothesis that a simple network, with three neurons and inhibitory gating, underlies the emergence of temporal tuning in the auditory midbrain. The slow kinetics of inhibition and postinhibitory rebound provide a basis for tuning to the long time intervals (10–50 ms) that are important in communication sounds. [Work supported by NIH Grant No. R01 DC01252.]
Ultrasound accelerates the healing of damaged peripheral nerves in vivo
Authors: Mourad Pierre D. , Curra Francesco , Crum Lawrence A. , Lazar Daniel A. , Kliot Michel
Published: July 2002

Peripheral nerve injury is a common clinical problem that often debilitates by producing significant motor and sensory deficits, as well as pain and other unpleasant sensations. Recovery is often slow. Patients with proximal injuries that require axons to regenerate over long distances to reach their target muscles or sensory receptors can take up to 2 years to recover function. Moreover, slow recovery can often be incomplete, due to the associated muscle atrophy, decrease in axonal regeneration along the pathway of the degenerating nerve, and decay in the axonal receptivity of the target tissues. In this work, we show that low-intensity therapeutic ultrasound can accelerate functional recovery in an animal model of a completely crushed peripheral nerve.