bluuebunny/crossref_metadata_2025 huggingface dataset:
Signaling characteristics of the surf zone acoustic communications channel
Authors: Preisig James C. , Partan James W. , Johnson Mark P.
Published: July 2002

The Near Shore Acoustic Network Experiment (NSANE) was conducted at the Scripps Pier in May 1999 to ascertain the physical properties of the very shallow water and surf zone environments which enable or constrain acoustic communications. Results of the analysis of the experimental data will be presented focusing on the properties of the environment which are of particular relevance to the performance of acoustic communications systems. Communications channel characteristics such as multipath spread, coherence time, and channel outage and signal attenuation characteristics will be examined. These characteristics will be related to observable environmental conditions and their effect on the performance of acoustic communications systems will be discussed.
Inverse problem of the wave equation and the Schwinger approximation
Authors: Hooshyar M. A. , Lam Tuan H. , Razavy M.
Published: July 2002

A new method of profile inversion for acoustic waves propagating in a medium with spherical inhomogeneity based on the Schwinger variational method is presented. The wave equation of interest is transformed into a Schrödinger equation, so that the Born approximation and the new method could also be applied at high frequencies. It is shown that the new method is stable and is more accurate than the Born approximation. To illustrate the method, an exactly solvable analytical example is presented. Also numerical examples using synthetic data, with and without additive noise, are given and the corresponding inversion results and the stability of the method are studied.
Environmentally adaptive wedge modes
Authors: Mignerey Peter C.
Published: July 2002

The notion of environmentally adaptive, curvilinear, uncoupled normal modes is developed by writing the Helmholtz equation in curvilinear coordinates. The depth-dependent vertical scaling function provides some coordinate freedom missing from the Cartesian formulation. This freedom permits adaptation of the normal mode approach to variable depth and variable sound-speed problems for environments that change slowly in range. A W.K.B. approximation to the eigenfunctions shows modal decoupling can be realized when the vertical scaling function is chosen equal to the reciprocal of the depth-dependent vertical wave number of the lowest mode. Numerical simulations demonstrate that a requirement for constant inter-modal ratios of the vertical wave number is valid throughout several wedges with different bottom boundary conditions. The horizontal refraction of such modes agrees closely with analytic solutions. For a wide-angle wedge, the acoustic field agrees qualitatively well with the benchmark solution of Dean and Buckingham [J. Acoust. Soc. Am. 93, 1319–1328 (1993)].
Analysis of resolution for an amplitude-steered array
Authors: Frazier Catherine H. , Hughes W. Jack , O’Brien William D.
Published: July 2002

In 1976, Hughes and Thompson introduced the idea of steering the maximum response of a linear array by amplitude weighting the output signals of the elements, thus eliminating the need for time delays or phase-shift networks. Currently that amplitude-steered array concept is being extended to a broadband two-dimensional array that can be used for real-time three-dimensional imaging. In shifting the use of the amplitude-steered array from underwater acoustic communications to imaging, we must consider different issues of the array’s performance such as lateral and axial resolution. For the linear amplitude-steered array, we show that both lateral and axial resolution are limited by the length of the array. The dependence of axial resolution on the length of the array is a unique feature of the amplitude-steered array, leading to an interesting tradeoff between lateral and axial resolution. A theoretical basis for the dependence is developed and simulation results are given.
Study of acoustic emission in a plate using laser ultrasonics and the finite element method
Authors: Shi Zhiqiang , Jarzynski Jacek , Jacobs Laurence
Published: July 2002

Acoustic emission (AE) is the spontaneous release of transient energy due to changes in localized stresses or incremental crack growth. This research studies AE generation, propagation, and detection in platelike components. The modeling of a variety of AE sources (such as micro-crack extension) and their resulting wave propagation signature, in a two-dimensional component, are investigated. The experimental technique features a laser-ultrasonic system for the point source generation and broadband, point-wise detection of elastic waves. The numerical algorithm uses the finite element method (FEM), which has the flexibility to simulate a variety of AE source types, and thus quantify source and geometric effects—geometric effects are specific component effects such as boundaries—on the predicted AE waveforms. These results provide a quantitative understanding of AE mechanisms, and assist in the interpretation of field-measured AE signals.
Internet audio as seen by the producer/musician
Authors: Somers Eric
Published: July 2002

In the battle over Internet audio transmission schemes, each format seeks to become the universal standard of the internet. Yet the author, a sound designer, composer, and producer, asserts that no one compression technology can best serve the various needs of the musician. The paper classifies these needs, suggests which schemes serve each best, and suggests musical and production issues that designers of audio compression technologies need to keep in mind.
Designing process plants to meet a noise limit based on verifying by a noise model rather than measurements
Authors: Brittain Frank
Published: July 2002

Normally, in the US process plants are designed to meet a noise limit based on verifying the limit has been met using noise measurements. An alternative approach is to design the plant based on confirming the noise limit has been met using a noise prediction model. The latter approach is often used in Europe and Australia. The strategy used in designing the plant depends in part on how meeting the noise limit is to be verified. Verification using a model has some distinct advantages and some disadvantages. The advantages of verification using a model include independence from variations in atmospheric conditions, and ambient levels (absolute and changes) at locations where the limit must be met. Verification using a model necessitates very close advance agreement among all parties on how the model is developed and approved. Further, the issues of experimentally verifying the model and updating the model with actual noise levels of equipment need to be addressed by all parties. These issues will be discussed, and alternative design strategies identified.
Using Caltrans noise analysis protocol methodology to determine insertion loss of classrooms at a high school
Authors: Greene Michael
Published: July 2002

The construction of a new freeway adjacent to an existing high school in eastern San Diego County, California, prompted the need for a rigorous analysis of the noise effects on the school. The insertion loss of structures (with windows and doors open and closed) at a high school was measured using the recently published California Department of Transportation (Caltrans) Noise Analysis Protocol. Both the school district and Caltrans agreed upon the details of the measurement methodology prior to the tests. The test setup consisted of two commercial-grade loudspeakers mounted atop a manually operated lift, associated amplifiers, pink-noise generator, a real-time noise analyzer, and sound-level meters. Noise levels were measured at equivalent distances in the absence of and then inside the room of interest, to derive the structure’s insertion loss. This was done at incident angles of 30, 45, 60, and 75 deg to the building façade. The resultant data from these measurements required the use of specially designed spreadsheets to effectively analyze and present the results. The results of the measurements indicated that improvements to the older classrooms near the freeway would be necessary in order to meet the indoor noise standard for classroom spaces.
Impulse propagation in granular media
Authors: Sen Surajit
Published: July 2002

Grains can be described as elastic objects. When two grains are pushed against one another, they repel via Hertz’ nonlinear force law, F∝δn, n>2, δ≥0, being the overlap between the grains. We show that the propagation of an impulse of any magnitude in a 1D chain of grains at zero loading can be described as a solitary wave. The width of the solitary wave, L(n)→1 as n→∞, L∼5 grain diameters for typical granular contacts and L(n)→∞ when n→2. The condition δ≥0 leads to the formation of secondary solitary waves when two identical solitary waves propagating in opposite directions collide. Randomness in grain densities and sizes and restitutional losses lead to approximately exponential decays in distance of the energy of a propagating solitary wave. It turns out that impulses can be exploited to fingerprint a buried impurity mass in a 1D chain with and without gravity. In closing, we shall discussthe backscattering of an impulse from a buried object in 3D beds at shallow depths. Implications of this work with respect to humanitarian demining and related applications will be presented. [Work supported in part by U.S. Army Corps of Engineers and Sandia National Laboratories. Work done in collaboration with Marian Manciu (SUNY-Buffalo) and Alan J. Hurd (Sandia National Labs).]
The noise from a crumpled candy wrapper as a probe of a disordered system
Authors: Kramer Eric M.
Published: July 2002

We discuss the origin and properties of the crackling sound emitted by a crumpled sheet of Mylar as it is strained. These sheets possess many qualitative features of a traditional disordered system, including frustration and discrete memory. The sound can be resolved into discrete clicks, which are emitted during rapid changes in the conformation of the sheet. Observed click energies range over six orders of magnitude. The measured energy autocorrelation function for the sound is consistent with a stretched exponential, C(t)=Aexp[−Bt0.35]. The probability distribution of click energies has a power law regime, p(E)∼1/E, independent of sheet size and material. We also discuss future directions for this research.
A laser-based ultrasonic technique to measure the dependence of the bending stiffness of copy paper on moisture and temperature
Authors: Griggs David A. , Berthelot Yves H.
Published: July 2002

A noncontact system is used to generate and detect, optically, a broadband ultrasonic pulse propagating in paper under controlled temperature and moisture conditions. The generation laser (Nd–Yag) produces a short optical pulse which is directed through an optical window on the paper sample inside an environmental chamber where temperature and relative humidity are controlled. Ultrasonic Lamb waves propagating in the paper are detected by a fiberoptic Mach–Zehnder interferometer (argon–ion laser) where the Doppler-shifted light exits the chamber through a small-core multimode fiber. The moisture content is measured by monitoring the weight of the paper sample relative to a dry sample. The dispersive nature of the A0 Lamb mode of the ultrasonic signal contains information about the bending stiffness normalized by the density and thickness of the paper averaged over the propagation path. The frequency dependence of the group velocity is found from the analytic wavelet transform of the signal (complex Morlet wavelet). [Work supported by the Department of Energy and the Institute of Paper Science and Technology.]
Growth of spectral contrast enhancement in Schroeder-phase harmonic complexes
Authors: Dreisbach Laura E. , Leek Marjorie R. , Lentz Jennifer J.
Published: July 2002

Discrimination of spectral differences in harmonic complexes is better for waveforms that are highly modulated and presented at high levels relative to lower-level stimuli with flatter temporal envelopes [M. R. Leek and V. Summers, J. Acoust. Soc. Am. 94, 2074–2082 (1993)]. This may reflect an enhancement of contrast between spectral peaks and valleys related to nonlinear cochlear processing. To further explore this relationship, discrimination of harmonic complexes with slightly different peak frequencies was measured at several stimulus levels. Peak-to-background differences required for discrimination were taken as a measure of the spectral contrast preserved in the auditory system. Phases were selected to generate either flat or peaked internal waveforms (negative or positive Schroeder phase), and peak frequency regions were near 2, 3, or 4 kHz. In normal-hearing listeners, the positive Schroeder waveforms produced lower spectral contrast thresholds than the negative Schroeder stimuli at all tested intensities and peak regions, with the greatest differences at moderate stimulus levels. Generally, hearing-impaired listeners demonstrated smaller threshold differences due to phase selection. These results are consistent with normal cochlear processing that is nonlinear at moderate levels, but more linear at low and high levels, and with more linear processing in impaired ears. [Work supported by NIH.]
Specificity of learning in an auditory temporal-order task
Authors: Wright Beverly A. , Mossbridge Julia A.
Published: July 2002

The ability to determine the onset order of two tones at different frequencies is a measure of temporal acuity and an analog of voice-onset time. Learning in this temporal-order task and its generalization to untrained frequencies and temporal-acuity tasks was explored. Temporal-order thresholds of six listeners trained 1 h per day for 6 days with tones at 0.25 and 4 kHz improved from 58 ms before to 12 ms after training, yielding a proportional improvement greater than on all untrained conditions. Comparisons between proportional improvements of trained and control listeners revealed that trained listeners learned considerably more than controls on the trained condition, and only slightly or no more than controls on: (1) the trained task at two sets of untrained frequencies (0.5 and 1.5 kHz, 0.75 and 1.25 kHz), and (2) three untrained temporal-acuity tasks (offset temporal order, onset asynchrony, offset asynchrony) at the trained frequencies. The lack of robust generalization to untrained frequencies and tasks suggests learning in onset temporal-order tasks is mediated by a frequency-dependent mechanism different from the mechanism(s) underlying performance in other temporal-acuity tasks. By increasing our understanding of plasticity in temporal-acuity mechanisms, these data may guide the treatment of related disorders. [Work supported by NIDCD.]
Causal recovery of the nonminimum phase from the measured magnitude of one-dimensional acoustic reflections
Authors: Clarke Cory L. , McDaniel J. Gregory
Published: July 2002

A new approach is presented for obtaining a reflection coefficient phase from magnitude using frequency-domain causality relations. This is useful because in many situations the reflection coefficient phase is more difficult to accurately measure than the magnitude; however, a knowledge of the phase is often vital to understanding the dynamics of the reflecting object. If a transfer function is minimum phase, then causality requires that its magnitude and phase are related by the Hilbert transform. Such relations do not exist for nonminimum phase-transfer functions. Previous work found that reflection coefficients are not necessarily minimum phase [McDaniel, J. Acoust. Soc. Am. 105, 2710–2716 (1999)]; however, the drive-point impedance of a passive reflecting object is. For one-dimensional systems, the drive-point impedance of the reflecting object is algebraically related to the reflection coefficient. The approach combines this relationship with causality relations for the impedance to find the complex reflection coefficient given only its magnitude. It is applied to analytic data for a one-dimensional structural acoustic system so that the actual phase may be compared to that predicted by the method. Extensions of the approach to multidimensional scattering will be discussed. [Work supported by ONR.]
The influence of substructure modeling on the predicted vibroacoustic response of a fluid-loaded plate system
Authors: Shepard W. Steve , Cunefare Kenneth A.
Published: July 2002

When predicting the vibroacoustic behavior of complex systems, one must decide how much effort to spend on modeling the features with dimensions smaller than those of the primary structure. To investigate these issues, this work examines changes in the vibroacoustic response of a semi-infinite fluid-loaded plate due to variations in modeling details associated with an attached substructure. The substructure consists of a smaller plate supported by springs along each edge. To examine the impact of spring scales, the manner in which the elasticity is distributed over the main plate is varied. Substructure modeling issues are examined by varying the number of degrees-of-freedom allowed in the substructure model. Both the combined system response and acoustic radiation from the main plate are computed using the Acoustic Surface Variational Principle and Hamilton’s Principle. Furthermore, sensitivity relationships that express changes in the system response to changes in the scale of the spring elements are presented. For the cases considered, it is shown that details associated with the scale of the spring element are only important for frequencies near or below the resonances of the isolated subsystem. Furthermore, only the dynamics of the substructure that includes rigid-body-type motions is important. [Work supported by Georgia Tech.]
Combining acoustic and electric hearing: Simulations and real-patient results
Authors: Turner Christopher W. , Gantz Bruce J. , Karsten Sue A. , Kwon Bom Jun
Published: July 2002

For patients with severe high-frequency sensorineural hearing loss, providing audible high-frequency, acoustic speech information often results in no increase, or in some cases a decrease, in speech recognition performance. One approach to this problem is to transmit the high-frequency speech information via a multichannel cochlear implant located in the base of the cochlea, while allowing the patient to continue to use the remaining low-frequency acoustic hearing. Data from simulation experiments are presented to show the amount of speech information that can be transmitted via this combination. The simulation of electric hearing was accomplished by using multiple channels of narrow-band noise modulated by the high-frequency speech signal. In general, speech recognition scores have the potential to be quite high if low-frequency (acoustic) information (below 500 or 1000 Hz) is combined with electrical stimulation for frequencies of 3000 Hz and above. An adverse effect of a mismatch between the speech frequencies and carrier band frequencies was observed, similar to the effect of assigning ‘‘wrong’’ frequencies to the cochlear implant. Some promising results from several human patients who have been implanted with this device are also shown. [Work supported by NIDCD.]
Bone conduction transmission and head-shadow effects for unilateral hearing losses fit with transcranial CIC hearing aids
Authors: Fagelson Marc A. , Noe Colleen , Blevins Jennifer , Murnane Owen
Published: July 2002

Bone conduction transmission and head-shadow effects were determined with transcranial completely-in-the-canal (TCCIC) CROS hearing aids. Five subjects with documented profound unilateral hearing loss and experience with traditional CROS/BICROS fittings (TCROS) were tested with a CIC hearing aid placed in their poorer ear. Peak SPL was measured at the tympanic membrane and ranged from 105–115 dB SPL at 2000 Hz. Pure-tone crossover thresholds and functional gain tested at frequencies from 250–8000 Hz varied considerably more than the SPL measures. The pure-tone results indicated that sensitivity in the better ear was moderately associated with functional gain across frequency. Speech recognition was then tested in the sound field in two conditions: direct (noise in the poorer ear, speech in the better ear) and indirect (noise in the better ear, speech in the poorer ear) at S/Ns of −6, 0, +6, +12, and quiet. The TCCIC fittings were more effective than TCROS aids across S/Ns, particularly in the direct condition. In the indirect condition, the two fittings performed similarly. When data were pooled across conditions, the TCCIC aids provided better word recognition than the TCROS aids, particularly for those subjects with greater sensitivity in the better ear.
Perception of prosodic phrasing by hard-of-hearing listeners
Authors: Barac-Cikoja Dragana , Revoile Sally , Waters Michelle
Published: July 2002

Severely to profoundly hard-of-hearing (HOH) listeners (n=12) were tested for their perception of prosodic phrase continuity in clear and conversational speech. In two experiments, fluently spoken sentences were compared with utterances artificially assembled from isolated words (experiment 1) and prosodic phrases (experiment 2) that replicated the sentences’ lexical composition. The difference in the overall duration of the assembled and fluent utterance was eliminated via signal processing, but the amplitude envelope and the intonational contour differences were left intact. Randomized repetitions of each utterance pair (72 pairs, 12 sentences × 2 speaking styles × 3 speakers, in experiment 1, and 40 pairs, 10 sentences × 2 speaking styles × 2 speakers, in experiment 2) were presented to each listener over several experimental sessions. In a 2IFC procedure, the listener identified the utterance that sounded more like fluent speech. Four normal-hearing (NH) controls were tested in white noise (S/N ratio=−20 dB). NH listeners identified the fluent sentences with accuracy greater than 90%. Across HOH listeners, identification accuracy varied from completely random to less than 75% correct, and was dependent on a listener’s sensation level and preferred communication mode (oral versus manual). [Work supported by NIDCD.]
Phonetic structure is similar across auditory and vibrotactile speech perception
Authors: Kello Christopher T. , Bernstein Lynne E.
Published: July 2002

Vibrotactile vocoders have long been viewed as a possible method for conveying speech information to deaf perceivers. However, modest levels of speech transmission have led to numerous alternative notions concerning limitations of vibrotactile devices. This study investigated whether perceived acoustic phonetic structure is preserved in the transformation of the F2 speech region via a linear vibrotactile vocoder array. In experiment 1, naive hearing subjects discriminated pairs of vibrotactile word stimuli immediately before and after 2 h of practice. At both times, relative vibrotactile discrimination levels were well predicted by identification of phonemes presented by an analogous F2 acoustic vocoder, suggesting that structure is preserved. In experiment 2, subjects separately rated auditory and vibrotactile consonant similarity of stimuli presented by auditory and vibrotactile vocoders, respectively. Analysis of phonological feature information showed similarities and differences in perceptual structure across modalities. Vibrotactile stimuli were rated to be more similar to each other than were auditory stimuli, suggesting that phonetic information was degraded relative to auditory information. Based on these results, current investigations are directed at methods for inducing perceptual learning of vibrotactile phonetic information. [Work supported by NIH/NIDCD 00695.]
Synthetic aperture processing to extract ocean bottom acoustic properties
Authors: Rajan Subramaniam D.
Published: July 2002

A review of an approach to determine ocean bottom acoustic properties in a shallow-water environment from data acquired on a synthetic aperture horizontal array will be presented. The performance of this method will be demonstrated using data from a number of field experiments. The feasibility of using this approach for rapid environment assessment will also be discussed.
Two-dimensional experimental analysis of tire vibration
Authors: Klos Jacob , Bernhard Robert J. , Cvar Paul
Published: July 2002

This paper presents an experimental analysis of the velocity response of a treadless tire in the two-dimensional wave-number domain. The out-of-plane velocity response was measured on a stationary tire using a Doppler laser vibrometer for a two-dimensional 2-cm by 2-cm grid of points over the frequency band from 70 to 1500 Hz. From the data, three distinct regions of behavior can be identified: simple standing wave patterns, waveguide behavior, and nearly cylindrical wave propagation. Using 2-D wave-number reduction techniques, the measured spatial velocity distribution at each frequency was transformed into 2-D wave-number space. Different wave types in the tire carcass can be identified including the dominant flexural and in-plane waves (due to Poisson’s strain). At frequencies below the ring frequency of the tire cross section, a qualitative comparison is made to published results for 2-D dispersion curves of cylinders. At higher frequencies, a comparison is made in the wave-number domain, to a coupled plate model of the tire carcass and models of wave behavior in inhomogeneous plates. A qualitative explanation of the behavior of the tire is identified from the comparisons.
Tire tread block noise experiments including effects of pavement porosity
Authors: Jones Sarah , Karnopp Dean , Sarigul-Klijn Nesrin
Published: July 2002

A tread block impact device has been developed to record the pressure pulse signature generated by a single tread block impacting a surface. High-speed video images are used to relate the impact progression with the instantaneous acoustic signal. The acoustic pressure pulses generating this device can be associated with the changing volume velocity of the air displaced as the tread block approaches the surface. A simple monopole source can be used to predict the acoustical pulse that is radiated from impact. Experimentation and theoretical calculations will be correlated, as well as discussion of previous research. Noise due to a sequence of blocks on a tire can be inferred from single pulse results and the sound power level can be examined as a function of the speed of the tire. By using impact surfaces with known area removal and, hence porosity, experimental relationships between the pressure pulse signature and impact surface characteristics can be determined. By evaluating the frequencies generated by tread block impacts and the effect of porosity on noise reduction, tuned pavements which could attenuate the most irritating frequencies could be developed. The theoretical and experimental models may prove useful in suggesting means of reducing this component of traffic noise.
Predicted ground effects for the sound fields near a reflecting wall
Authors: Tang Raymond S. H. , Li Kai Ming
Published: July 2002

In many environmental noise prediction schemes, an empirical correction factor of 2.5 or 3.0 dB(A) is to be added for the calculation of noise 1 m in front of a reflecting facade. In this paper, theoretical and experimental studies have been conducted to examine the validity and accuracy of such approximations. The theoretical analysis is based on the representation of the sound waves in their integral forms. By imposing the impedance boundary conditions on the absorbing ground and the vertical wall, it is possible to extend the classical Weyl–Van der Pol formula for inclusion of the effect of a reflecting facade. As expected, the analytical solution is composed of four terms (a source and three image sources) as a result of the absorbing ground and the reflecting facade. Experimental measurements have been conducted indoors to validate the theoretical predictions. It has been demonstrated that the simple empirical correction factor is not adequate in most cases for the assessment of the facade noise levels above an absorbing ground. [Work supported by the Hong Kong Polytechnic University.]
Implementation of high-quality text-to-speech synthesis for limited domain applications
Authors: Shukla Sunil R. , Barnwell Thomas P.
Published: July 2002

Though current TTS systems can produce unrestricted, intelligible speech using a limited database of prerecorded sounds, the quality of speech is highly artificial. By using larger speech segments, such as a combination of words and diphones, the number of segment boundaries are reduced drastically, resulting in high-quality TTS that has a humanlike natural voice. Such a system can be useful for limited domain applications such as driving directions, weather advisories, etc. Experiments were conducted to generate natural sounding speech from words and diphones by modifying the pitch and duration of the units to match the prosody characteristics. The Festival TTS system, developed at the CSTR at the University of Edinburgh, was used to aid in the implementation of the experiments. The method for synthesis is pitch-synchronous residual LP. This method allows for producing smooth transitions between segments. A database of residuals and parameters for segments (words and diphones) is prepared. During synthesis, the segments are concatenated and the desired prosody is matched using time-domain modifications of pitch and duration. Using natural prosody, waveforms were synthesized, resulting in close to natural sounding speech. This demonstrates synthesized speech can sound identical to the original speaker, given the correct prosody.
Harmonic imaging in tissue
Authors: Routh Helen
Published: July 2002

In the last few years it has become clear that harmonic imaging in tissue (or tissue harmonic imaging) will improve image quality in many ‘‘difficult to image’’ patients. This talk will focus on the practical and clinical aspects of this imaging method which makes use of the nonlinear propagation of ultrasound in tissue. By filtering the received signal around the second harmonic, much of the haze and clutter in the image is reduced. Although there has been much research on the propagation of nonlinear waves in tissue, the exact mechanisms of this image quality improvement are still unclear. One hypothesis is based on the fact that the intensity of the second harmonic signal increases as the signal pass deeper into tissue. As the majority of artifacts arise from structures close to the transducer, the artifacts in the second harmonic signal are significantly lower than those in the fundamental. By imaging the second harmonic signal, much of the haze and clutter in the image can then be reduced. This talk will give a basic description of tissue harmonic imaging illustrated with clinical examples and a hypothesis for the improvements in image quality.
Dynamic sonoelastography—Making the impossible, possible
Authors: Levinson Stephen F. , Fu Dongshan , Parker Kevin J. , Gracewski Sheryl M.
Published: July 2002

Sonoelastography refers to the use of ultrasound to image the viscoelastic properties of soft tissues. Although a number of techniques have emerged, most are qualitative and static in nature. The availability of dynamic quantitative methods could open a new field of functional imaging for the study of biomechanics. We have developed an approach using 2D speckle tracking and finite element-based elastic modulus reconstruction. The speckle tracking method uses a deformable mesh with nodes assigned to points with a high feature content. The tissue is harmonically excited at a frequency of less than 100 Hz and vibration vectors are obtained at the nodes of the mesh. Young’s modulus is then obtained within a series of small regions of interest using an iterative forward estimation approach. In each region, a finite element algorithm is used to predict the internal displacements from the measured motion on the boundary. A sum squared difference operator is used to estimate the associated error, from which an improved Young’s modulus is obtained for use in the next iteration. Results from simulations and from measurements in soft tissue phantoms and in human muscle will be presented. Limitations of the technique will be discussed along with potential solutions.
The application of a material parameter extraction algorithm to MRI-based displacement measurements
Authors: Romano Anthony J. , Bucaro Joseph A. , Ehman Richard L.
Published: July 2002

A novel algorithm based on the variational formulation is presented for the determination of the material parameters (λ+2μ)/ρ and μ/ρ throughout inhomogeneous media given volumetric displacement information. The performance of the inversion algorithm is subsequently investigated when applied to measured displacement data throughout an inhomogeneous test phantom. The vector displacement components throughout the test phantom subject to monochromatic shear excitation measured in time using MRI (Magnetic Resonance Imaging) were temporally Fourier transformed to extract the components of monochromatic excitation, and the data were delivered to the inversion algorithm. A sequence of studies is presented on the basis of subsequent wavenumber filtering, polarization selection, and variation in the size of the volume elements of resolution. The resulting performance is assessed and recommendations for future efforts are discussed. [Work supported by ONR and NIH.]
Comparison of minor to major loop properties in PMN-PT ceramics
Authors: Robinson Harold C. , McLaughlin Elizabeth A.
Published: July 2002

The electromechanical properties of lead magnesium niobate-lead titanate (PMN-PT) ceramics are of great interest to transducer designers. Typically, the strain versus electric field and polarization versus electric field curves used to obtain those properties are measured over a major loop, i.e., one with a large dc bias and large ac signal. However, many devices are designed to operate at lower fields that fall entirely within the major loop, i.e., in a minor loop. Since the electromechanical properties of PMN-PT are strong functions of the bias and drive levels, it is crucial to understand how well properties derived from the major loop measurement correspond to the actual minor loop properties. In this study, electromechanical measurements on PMN-PT corresponding to minor loops at varying dc bias, ac drive, mechanical prestress, and temperature levels were made. The equivalent piezoelectric constant, dielectric constant, and dielectric loss factor for these minor loops will be compared to the corresponding major loop parameters. It will be shown that, in many cases, the parameters derived from the major loop agree quite well with the directly measured minor loops. An attempt to establish the lower limit for extracting minor loop properties from major loop data will be made.
Application of nonlinear wave processes for the nondestructive characterization of adhesives
Authors: Meurer Thomas , Jacobs Laurence , Qu Jianmin
Published: July 2002

This study investigates the mechanics and mathematical fundamentals of the propagation of nonlinear ultrasonic waves in adhesives. The objective of this research is to develop an understanding of the underlying mechanics of nonlinear waves, in order to develop quantitative techniques capable of interrogating damaged adhesive bonds. This study develops a mathematical model that represents a nonlinear stress–strain relationship, hysteresis, and then applies it to one-dimensional wave propagation. The numerical procedure uses a finite-difference scheme to study the propagation of pulses in this nonlinear media. This research includes an experimental verification of these numerical results, as well as a physical interpretation.
Generation and propagation of acoustic Bessel bullets
Authors: Stepanishen Peter
Published: July 2002

Acoustic Bessel bullets are a new class of localized wave solutions to the linearized wave equation with controllable spectral properties. Ideally such waves maintain their spatially dependent shape and time history as they propagate in free space. A brief review of the history of acoustic Bessel bullets (BBs) will be first presented. Both Fourier transform and recently developed convolution and impulse response methods of investigating the space–time properties of acoustic BBs will be presented. The generation of acoustic BBs from an array of planar annular rings with appropriate space–time source excitations will be addressed via the use of the space–time Kirchhoff integral solution. Various properties of acoustic BBs generated from an infinite planar aperture will be presented and contrasted to the space–time characteristics of the acoustic BB’s generated by a finite planar aperature—the latter exhibits the characteristics of the former over a limited space–time region. The supersonic nature of the on-axis acoustic BB fields will be simply explained using space–time characteristics of the source excitations. Numerical results will be presented to illustrate the tradeoffs between the radial extent and the near- to far-field transition of acoustic BBs, and several interesting characteristics of the far field will also be discussed.
Effect of high-intensity focused ultrasound on platelet activation, aggregation, and adhesion
Authors: Poliachik Sandra L. , Mourad Pierre D. , Crum Lawrence A. , Chandler Wayne L.
Published: July 2002

High-intensity focused ultrasound (HIFU) has been examined as a noninvasive means for achieving acoustic hemostasis [Delon-Martin et al., UMB 21, 113–119 (1995); Hynynen et al., UMB 22, 193–201 (1996); Vaezy et al., UMB 24, 903–910 (1998)]. Our own efforts in acoustic hemostasis are directed toward using diagnostic ultrasound to locate a hemorrhage and HIFU to halt the bleeding. To enhance the imaging of blood, the use of ultrasound contrast agents (UCAs; gas-filled microbubbles that increase the echogenicity of fluids) has been proposed as a means to locate internal bleeding; however, the combination of UCAs and ultrasound has been found to cause bioeffects in whole blood [Miller et al., UMB 23, 625–633 (1997); Poliachik et al., UMB 25, 991–998 (1999)]. Our results have shown that HIFU can cause platelets in a platelet rich plasma (PRP) sample to activate, aggregate, and adhere to a collagen-coated surface. Furthermore, UCAs can increase the amount of cavitation induced by HIFU, and thus lead to an increase in platelet activity. Although HIFU exposure alone can induce platelet activity, the addition of UCAs increases the amount and the rate of cavitation (cavitation dose); therefore, cavitation is the likely mechanism of HIFU-induced platelet activity. [Research supported by DARPA.]
Acoustic modeling of miniature loudspeakers
Authors: Herrera Guillermo , Sommerfeldt Scott D.
Published: July 2002

There is currently considerable interest in developing models that more accurately predict the response of systems with small loudspeakers, such as in cellular telephones. There has also been a trend towards developing hands-free communication with cell phones, thus requiring a relatively high acoustic output from a small source. Work will be reported on the development of a model for a cell phone to help address such research issues. It has been shown that boundary layer effects can cause significant frequency shifts in the resonance peaks associated with systems having elements with dimensions on the order of the boundary layer thickness. This phenomena has been observed in the presence of ports with diameter of 1 mm and less. These effects are being investigated in a cell-phone system, and the results obtained to date will be presented.
Functional changes in the ear with old age: A review
Authors: Schmiedt Richard A. , Lang Hainan
Published: July 2002

To study the true effects of age on hearing, one needs a model wherein environmental noise and genetic influences can be controlled over the lifetime of the animal. Popular models include various mice and rat genotypes, gerbils, and rabbits. All models show varying degrees of hair-cell loss, spiral ganglion cell (neural) loss, and atrophy of the stria vascularis with age. Animals raised in quiet show little loss of hair cells, and cochlear nonlinearities remain intact, except for those genotypes that are known to have progressive hair-cell loss, like the C57BL/6 mouse. On the other hand, all models show strial atrophy and neuronal loss with age. Functional consequences of strial atrophy include a decreased endocochlear potential and an altered ionic homeostasis within the cochlear duct. Neuronal loss may preferentially affect cochlear afferent neurons with low spontaneous rates and high thresholds. Indeed, the loss of the endocochlear potential may correlate with the inactivity of these neurons, even in young animals. Thus, strial atrophy may induce changes in the activity of specific neuronal populations, thereby changing not only hearing thresholds, but also how sound is encoded at suprathreshold levels. [Work supported by NIA.]
Physiological correlates of presbycusis: Single-neuron recordings in awake animals
Authors: Walton Joseph P.
Published: July 2002

During aging, the brain undergoes senescence alterations causing a decrease in many behaviorial responses, including the perception of complex sounds in difficult listening situations. Two neural deficits are likely responsible. One is a loss in sensory cells in the inner ear, while the second is likely due to deficits in neural processing within the central auditory system. This presentation will address the question as to whether evidence exists to support the idea of age-related deficits in auditory processing in the brain. Initial studies were devoted to the inferior colliculus (IC), an important midbrain nucleus that integrates information from many lower brainstem centers. We used two experimental approaches to assess neural encoding of complex signals. First, temporal processing of static (gap detection) and dynamic (amplitude modulation) changes in sound intensity in single neurons from young and old animals was examined. Results demonstrate that encoding of sound temporal features in many aged neurons is degraded. Second, we applied neurotransmitter antagonists microiontophoretically to young IC neurons to degrade temporal coding ability. The results display a wide range of complexities, but in some neurons temporal encoding is markedly disrupted. [Work supported by NIA–NIH, and the International Center for Hearing & Speech Research.]
Progressive hearing loss in mouse models of presbycusis: Influence of an augmented acoustic environment and of gender
Authors: Willott James F.
Published: July 2002

Progressive hearing loss associated with aging can be modulated by a number of genetic and environmental variables. Understanding how such variables work may suggest new approaches to ameliorate presbycusis. Two examples are long-term exposure to an augmented acoustic environment (AAE) and factors associated with gender (e.g., during the period of reproductive decline in females after 6 months of age). Research on inbred strains of mice that exhibit progressive hearing loss (C57BL/6J, BALB/cJ, DBA/2J) has demonstrated that daily exposure to a 70-dB SPL broadband noise AAE slows the progressive elevation of ABR thresholds, enhances behavioral responses to tones (startle response; prepulse inhibition), and affects histopathology of the cochlea and anteroventral cochlear nucleus (AVCN). However, gender plays a role in both the progression of hearing loss in nonexposed mice and the effects of the AAE. In the absence of AAE exposure, young C57BL/6J and BALB/cJ males and females have similar ABR thresholds, but hearing loss deteriorates more rapidly in females after around age 6 months. The auditory systems of males and females also respond differently to the AAE. Depending on gender, both positive and negative effects of AAE exposure are observed, although these effects are complicated.
Analysis of reconstruction of radiated acoustic pressure fields by using the HELS method
Authors: Rayess Nassif , Wu Sean
Published: July 2002

This paper presents a detailed analysis of reconstruction of the acoustic pressure fields radiated from a partially vibrating sphere by using the Helmholtz equation-least squares (HELS) method [Z. Wang and S. F. Wu, J. Acoust. Soc. Am. 102, 2020–2032 (1997); 104, 2054–2060 (1998)]. The objectives of this study are to gain insight into an acoustic inverse problem and to develop guidelines that may be helpful in the future reconstruction work. Because of the complexities involved, many questions such as where and how many measurements should be taken, how many expansion terms are necessary for a given number of measurements, etc., remain unanswered. These questions will be tackled here. The reasons for selecting a partially vibrating sphere are twofold: (1) the resulting acoustic pressure field contains a very pronounced near-field effect; and (2) analytic results are known so the reconstructed acoustic pressures can be checked rigorously. The impact of a loss of the near-field effect on reconstruction will be investigated. The effects of measurement distance, area, and shape on the accuracy of reconstruction will be examined. The efficiency of reconstruction using the HELS method as the increase in frequency will also be studied. [Work supported by the NSF, Grant No. CMS-9802847.]
Acoustics and perception of Russian plain-palatalized contrast
Authors: Kochetov Alexei
Published: July 2002

Acoustic and perceptual correlates of Russian syllable-final plain and palatalized coronal stops were investigated. The acoustic analysis based on the data from six talkers showed that the stops were consistently released both word-finally and before stops. Both consonants in final position were strongly affricated and aspirated. The VC transitions to palatalized stops extended for more than half of the vowel, substantially affecting its quality. The perception experiment (12 listeners) determined that both bursts and transitions were perceptually relevant to the identification of the two phonemes. The contrast in final and preconsonantal environments differed in the relative importance of these cues: VC transition was more important for the plain-palatalized distinction in final position, while burst was a major cue to the contrast in preconsonantal position. The findings suggest that the presence of the plain-palatalized phonemic contrast in perceptually less favorable syllable coda positions is compensated for by additional acoustic information that assists a listener in the recoverability of the contrast. [Work supported by Social Sciences and Humanities Research Council of Canada.]
Effects of syllable structure and syllable boundary on segment duration in Seoul Korean
Authors: Lim Byung-jin
Published: July 2002

The present study reports results of an investigation into Korean durational patterns with respect to syllable structure and syllable boundary. The main questions raised in this study were (1) whether different preceding syllable structures contribute to the durational patterns of the following segmental durations: closure duration, voice onset timing (VOT), and vowel duration; and, if so, (2) how they are realized, especially over syllable boundaries determined by Korean orthography. Thirty-six two-syllable nonsense words varying in syllable structure were analyzed. For the durational pattern of internal elements of syllables over syllable boundary, the initial consonants of the second syllable were differentiated into lax, tensed, and aspirated stops. Results indicate that initial consonant duration showed no significant difference regardless of syllable structure. Initial vowel duration, however, reflected temporal compensation depending on the syllable structure. In addition, the effect of preceding syllable structure was reflected only on the closure duration, not on the VOT nor on the vowel durations of following syllables. These findings imply that temporal compensation tends to occur across segments over syllable boundaries, suggesting the importance of syllable boundary in durational patterns in Seoul Korean. The relevance of orthography to syllable boundary is also discussed.