bluuebunny/crossref_metadata_2025 huggingface dataset:
High resolution ultrasound imaging system for soft tissues
Authors: Ye S. G. , Liu X. Z. , Gong X. F. , Zhang W. Y. , Jia Y. Q. , Tan X. Y.
Published: July 2002

The great interest in high resolution (higher than 0.1 mm axially and 0.3 mm laterally) ultrasound imaging systems for application to the skin, eye, intestinal wall, etc., gives rise to the development of a high resolution ultrasound imaging system. In this study, the high resolution ultrasound imaging system with a frequency range from 20 to 40 MHz was developed. In the system described here, the different resolutions were obtained by means of the focused transducers with different center frequencies in the frequency range mentioned above. In designing and fabricating the PVDF transducer, the KLM equivalent circuit including internal loss was developed and the influence of the PVDF film and backing materials on the transducer characteristics were analyzed as well. The experimental results were compared with the analyzed results. High resolution ultrasound imaging of some soft tissue samples was obtained. Besides the ultrasound parameters such as speed of sound, the attenuation coefficient and backscattering coefficient were measured in the frequency range from 20 to 40 MHz. [Work supported by NSF of Jiangsu Province, China.]
Interarticulator phasing and locus equations
Authors: Lofqvist Anders
Published: July 2002

A locus equation plots the frequency of the second formant at vowel onset against the target frequency of the same formant for the vowel in a consonant–vowel sequence. The slope of the equation has been assumed to reflect the degree of coarticulation between the consonant and the vowel, with higher slopes associated with more coarticulation. This study examined the articulatory basis for this assumption, using VCV sequences where the consonant was a bilabial stop /p, b/ and the vowels one of /i, a, u/. Articulatory movements were recorded using a magnetometer system. Four subjects participated and produced ten repetitions of each sequence. One articulatory measure was the temporal phasing between the onset of the lip closing movement and the onset of the tongue body movement from the first to the second vowel. Another was the magnitude of the tongue movement from the onset of the second vowel to the tongue position for the vowel, averaged across four receivers placed on the tongue. When compared with the corresponding locus equation slopes, neither measure showed support for the assumption that the slope serves as an index of the degree of coarticulation between the consonant and the vowel. [Work supported by NIH.]
Phonetic categories: Internal category structure and processing speed
Authors: Miller Joanne L. , Elimas Peter D. , Cox Ethan
Published: July 2002

Phonetic categories have a graded internal structure, with some members perceived as better exemplars than others. In a project focusing on voiceless stop consonants, the relation between this structure and processing speed has been examined. Speech continua were constructed in which the voice-onset-time (VOT) value of a word-initial consonant systematically changed from very short to very long. Unspeeded identification tests confirmed that stimuli with very short VOT values are perceived as voiced, whereas those with longer VOT values are perceived as voiceless. Category-goodness rating tests further confirmed that only stimuli within a limit range along each continuum are perceived as good exemplars of the voiceless category; stimuli with shorter or longer VOT values are perceived as poorer exemplars. Initial results from an ongoing experiment involving speeded identification indicate that (1) compared to the best exemplars of the voiceless category, identification of poor exemplars in the voiced–voiceless boundary region is relatively slow, but (2) across a wide range of values, poor exemplars with VOT values longer than the best exemplars are identified as quickly as the best exemplars themselves. These initial findings indicate that internal category structure is not necessarily reflected in processing speed. [Work supported by NIH.]
Using Doppler ultrasound to detect wall vibrations and flow velocity fluctuations in arteries
Authors: Plett Melani I. , Beach Kirk W. , Paun Marla
Published: July 2002

Two arterial disorders, stenoses and perforations, result in fluctuations in both wall displacements and blood velocities that are not displayed by conventional ultrasound instruments. Wall vibrations with amplitudes on the order of a micron are too small to be displayed by M-mode. Narrow-band velocity oscillations of less than 50-ms duration can easily be missed in viewing traditional Doppler spectral waveforms. Low-frequency velocity oscillations are attenuated by wall filters. Furthermore, the temporal relationship between flow velocities and wall displacements is not avail- able in conventional systems, yet this relationship provides key information in studying stenoses and locating perforations. To simultaneously examine flow velocities and wall displacements in arteries, a customized ultrasonic, pulse-echo, multigate, quadrature phase demodulation system has been developed. The use of multigate, quadrature phase demodulation in the absence of a wall filter enables exploration of arterial behaviors temporally in the cardiac cycle with sufficient amplitude, frequency, and duration resolution to meet the rigorous demands of the analysis. Wall vibrations as high as 600 Hz with amplitudes less than a micron have been detected simultaneously with arterial jet velocities and flow oscillations. [This work was supported by a grant from DARPA, No. N00014-96-0630.]
A free-flooding rare-earth iron hexagonal transducer
Authors: Zhao Rong Rong
Published: July 2002

This paper describes the development of a free-flooding rare-earth iron hexagonal transducer with an outer size of φ160×160 and a weight of 4.9 kg. The vibrations of the rare-earth iron hexagonal transducer and the free-flooding water cavity in it are theoretically analyzed and discussed. The measurement result shows that the transducer may send out a source level of 185 dB, and the resonance frequency of the transducer drops down from 1.90 kHz in air to 0.85 kHz in water because of the cavity resonance. The free-flooding water cavity can therefore not only withstand the hydropressure, but also make the resonance frequency drop down considerably. The free-flooding rare-earth iron hexagonal transducer shows promise to be a lightweight, high-power sound source for operation at great depths in the ocean. [Work supported by CSSC.]
Lemur: A bandwidth-enhanced sinusoidal modeling system
Authors: Fitz Kelly , Haken Lippold
Published: July 2002

Lemur models sounds as a collection of partials having amplitude, bandwidth, and frequency envelopes. Bandwidth envelopes allow the neat representation of noisy parts of sounds which produce clutter in purely sinusoidal analyses. Lemur associates noise energy with sinusoidal components that are nearby in frequency. Bandwidth envelopes record the fraction of the partial energy that is attributable to noise energy, as opposed to sinusoidal energy. Amplitude envelopes are calculated to include the energy added by the bandwidth association process. When partials are pruned from the model, in the analysis process or during editing, Lemur preserves the overall energy by distributing the removed partials energy among neighboring partials. For sounds with a good spread (in frequency) of partials, Lemur can represent noise energy in the appropriate spectral regions while retaining the manipulability and homogeneity of a purely sinusoidal model. This homogeneity is important for implementing certain kinds of model-domain behaviors and real-time timbral manipulation. Lemurs synthesis includes a spectral line widening technique to spread energy away from each partial’s center frequency according to bandwidth envelope values.
Timbre morphing and interpolation based on a sinusoidal model
Authors: Osaka Naotoshi
Published: July 2002

There have been several attempts to synthesize the timbre in between two sounds. Several synthesis methods are reported to work well, but are not automatic throughout the whole process or are not precisely described if one wishes to trace the algorithm. An automatic algorithm of synthesizing morphed sounds and interpolated timbre has been reported. Two original sounds are analyzed using the M&Q algorithm. Correspondent partials of each sound are found using Dynamic Programming. Two synthesis methods are introduced using a sinusoidal model. One is to find correspondent partials within correspondent frames of two sounds. Then an interpolated partial of a new frame is calculated. Peak-to-peak match of sinusoidal parameters is done for a new frame and synthesized sounds are acquired. The other method is the one which changes the procedure sequence of the first method. Correspondence is considered for sequent partials and not a framewise signal. These two methods are compared with another simple synthesis method, that is, wave-to-wave interpolation of one pitch period. Total performance of sounds are discussed using subjective test results.
Study of noise levels in a neonatal intensive care unit
Authors: Laroche Chantal , Fournier Paula
Published: July 2002

In the past few years, much interest has been focused on the integrated care approach, where noise is seen as an element which can compromise the normal development of newborns in neonatal intensive care units. The objective of this study was to develop a methodology evaluating the impact of training of the nurses, regarding noise levels existent within the neonatal intensive units of an Ottawa regional hospital. The method consisted of continuous noise level measurements performed by a computer (type 1 sound level meter), pre- and posttraining. LAeq,1sec, as well as audio samples were recorded throughout eight work shifts. The average pretraining A-weighted noise levels were of 53, 61, and 65 dB, for the night, day, and evening shifts, respectively. These levels largely exceed the maximal A-weighted sound level of 45 dB, recommended by the World Health Organization to avoid negative effects on sleep. Throughout this study, it is likely that the training of nurses could contribute to the reduction of noise levels, but that interventions concerning noise control would also be necessary in order to ensure an acceptable sonorous ambiance for neonates requiring intensive care. [Work supported by University of Ottawa.]
Ultrasonic three-dimensional probe modeling in anisotropic solids
Authors: Niklasson A. Jonas
Published: July 2002

Three-dimensional wave propagation and probe modeling in a homogeneous, linear elastic, anisotropic half-space is discussed. The probe is modeled by modifying the traction vector at the interface between an isotropic half-space and an anisotropic half-space. The traction vector is obtained by considering a plane wave in the isotropic solid incident upon the interface. The probe can be of any type, angle, frequency, and size. The probe is attached to an anisotropic half-space and the wave propagation problem is solved by means of Fourier transform techniques. Numerical examples illustrate some of the properties of the probe model and wave propagation in anisotropic solids.
Modal excitation and control of membrane waves on cylindrical shells
Authors: Bondaryk Joseph E.
Published: July 2002

A set of in-air experiments were made on two, thin, cylindrical shells to understand and control the propagation of membrane waves, which are primary determinants of target strength in the mid-frequency, high-aspect angle regimes. A circumferential source array was used to drive single modes in all wave types, compressional, shear, and flexural. Resulting waves were collected using an axial line array of laser Doppler velocimeter measurements and the wave types separated by array processing. Comparison between a clean plastic shell and a steel shell with a keel-like feature suggest on the order of 10-dB reduction of compressional wave response via coupling into higher order flexural waves by the nonaxisymmetric discontinuity. The conversion coupled with subsequent damping of the resulting flexural waves makes this a potentially useful mechanism for control of membrane waves.
Comments on “A re-examination of risk estimates from the NIOSH Occupational Noise and Hearing Survey” [J. Acoust. Soc. Am. 101, 950–963 (1997)]
Authors: Dobie Robert A.
Published: July 2002

The recent paper by [J. Acoust. Soc. Am. 101, 950–963 (1997)] uses as a primary outcome measure an estimate of hearing handicap based on a weighted average of pure tone thresholds at 1, 2, 3, and 4 kHz. This choice is unusual and inadequately justified. If four equally weighted frequencies are to be chosen, the ANSI standard referenced by Prince et al. would suggest 0.5, 1, 2, and 4 kHz. If 1, 2, 3, and 4 kHz are chosen, the weights from ANSI 3.5, 1969 would be very different from those used by Prince et al.
Spatial impression as measured in concert and opera auditoria
Authors: Barron Michael
Published: July 2002

A coherent set of subjective experiments (published in 1973 and 1981) established the effect of spatial impression associated with early lateral reflections. The early lateral energy fraction was proposed as an objective measure. Some authors have preferred to use measures linked to cross correlation, presumably on the basis that this is probably closer to the mechanism used by the ear. The paper reviews the results of measurements of the early lateral energy fraction in 17 British concert spaces, as well as considering the measured results by Bradley in 13 North American concert halls. The discussion considers the relationship between early lateral energy fraction and hall width, the behavior of the measure close to the source and in both parallel-sided halls and fan-shaped halls. The design requirements for high spatial impression are also considered. The subjective effect of early lateral reflections is also influenced by sound level. The consequences for design of considering this additional variable in combination with the directional distribution will also be discussed. Spatial impression in concert halls and opera houses will be examined.
Modal leakage in range-dependent oceans
Authors: Baggeroer Arthur B. , Scheer Edward K.
Published: July 2002

The validity of the adiabatic approximation for modal propagation at low frequencies and over long megameter ranges is evaluated. A dynamical ocean model for the sound speed profile perturbations is superimposed upon a canonical Munk profile to represent a range-dependent ocean. The channel is excited with a single mode and propagated with the Collin’s FEPE code which was tuned to conserve the energy in each mode in a range-independent ocean. Modal amplitudes were determined by projecting the field on the local range-dependent modes. If one uses displacements which correspond to nominal experimental levels in the Atlantic, mode coherence is maintained only for ranges less than 1 megameter at 75 Hz; the energy appears to approach equipartitioning. Results starting with mode 1 and mode 10 were qualitatively the same. If the displacements are reduced by a factor of three, possibly more representative of Pacific levels, modal coherence is maintained for more than four megameters.
Additive effects of phonetic distinctions in word learning
Authors: Pater Joseph V. , Stager Christine L. , Werker Janet F.
Published: July 2002

While infants have been demonstrated to be sensitive to a wide variety of phonetic contrasts when tested in speech discrimination tasks [Eimas et al. (1971) et seq.], recent work [Stager and Werker (1997)] has shown that following habituation to a word–object pairing, infants of 14 months fail to notice when the place of articulation of the initial consonant is switched [b/d]. Using the same procedure, the present study has found that infants do not respond to a change in voicing [b/p]. They do, however, notice a switch between dissimilar words [lɪf/nim]. One interpretation of these findings is that 14-month-olds do not encode either place or voice distinctions in lexical representations, so that words differing in only these features are treated as identical. To test this hypothesis, the effect of combining featural contrasts is currently being investigated by examining whether infants do respond to a change in both place and voice [d/p]. If there is such an additive effect, the contrasts must be represented. This would entail that an explanation for the failure to distinguish words differing in only a single feature should invoke processing factors, rather than representational ones.
Radio frequency hearing: Electrostrictive detection and bone conduction
Authors: Bennett Wm. R.
Published: July 2002

A hearing aid patented by C. R. Schafer and supposedly based on detection of an amplitude-modulated carrier wave in the auditory cortex was re-examined. It is shown here that the hearing aid actually works by bone conduction of sound. It is concluded that detection of the modulation signal occurs by electrical nonlinearities and electrostriction in the bones of the face and skull.
Temperature dependence of ultrasonic Grüneisen parameter and ultrasonic attenuation in alkali halides
Authors: Sahasrabudhe G. G. , Lambade S. D.
Published: July 2002

Temperature dependence of ultrasonic attenuation and ultrasonic Gruneisen parameter are investigated in alkali halides in the range 80–300 K. The calculations use a computer program, developed by the authors, for implementing Nava’s modified formulation of Woodruff’s theory. These calculations are done for NaCl, NaF, and LiF for longitudinal and shear waves along the [100], [110], and [111] directions. Compared to calculations based on original Mason formulation, it was found that in most cases the results are in better agreement with the experimental data. The results also help to throw some light on relative merits of different theories of attenuation.
The impact of anisotropic roughness on acoustic interaction with the seafloor
Authors: Lyons Anthony P. , Pouliquen Eric , Fox Warren L. J. , Thomson Patricia A. G.
Published: July 2002

Accurate description of small scale sediment roughness and its dynamics plays an essential role in the understanding of high-frequency acoustic interaction with the seafloor. The influence of surface waves can be very strong in shallow water, commonly producing relatively large, oriented, and quasi-periodic sediment features, i.e., ripple fields. One-dimensional analysis, which can be limiting in the study of anisotropic seafloors, has traditionally been used to describe sediment roughness spectra. Due to the windowing and averaging operations used to reduce bias at higher spatial frequencies, these studies have usually missed the small bandwidth components that exist. This talk will focus on seafloor roughness and acoustic measurements taken recently on rippled seafloors near Elba Island, Italy. Results of high-resolution two-dimensional roughness measurements obtained with a fully digital close-range photogrammetry system will be presented and compared with previous descriptions of roughness spectra. Acoustic backscatter and penetration measurements, which show a definite sensitivity to the anisotropic nature of the seafloor, will be compared to models that incorporate the measured ripple structure.
Scattering due to bioturbation in marine sediments
Authors: Jones Chistopher D. , Jackson Darrell R.
Published: July 2002

Biologically active sediments are continually modified by epifauna (organisms that live on the sediment surface) and infauna (organisms living within the sediment). The collective mixing effect of these organisms is termed bioturbation. Bioturbation is pervasive and significantly affects the acoustic scattering characteristics of the seafloor. Epifaunal activity, such as locomotion and home building, creates roughness at the sediment-water interface. Infaunal activity, such as tube building, is responsible for the vertical and horizontal redistribution of solid material within the volume of the sediment, creating spatial and temporal inhomogeneities in sediment bulk properties (density, porosity, and compressibility). Classical diagenetic models describe bioturbational mixing as an idealized mass balance between adjacent layers of sediment. A proposed extension is to describe mixing as a stochastic forced diffusion process. The temporal and spatial spectrum of fluctuations in the sediment density and interface roughness are then found by modeling the biological forcing as a filtered Poisson process. By coupling the bioturbation model with scattering models, the effects of biological activity on acoustic scattering from the sea- floor can be studied. Applications include the remote sensing of benthic biology and the time evolution of targets on the seafloor. [Work supported by ONR.]
On the statistical characteristics of a flow noise field inside a flexible liquid-filled cylindrical array
Authors: Aronov Boris , Brown David A.
Published: July 2002

The statistical characteristics of the flow noise field inside a flexible liquid-filled axially streamlined array are considered. General expressions are obtained for the flow noise cross-spectral density and coherence function. The coherence function and the gain in signal-to-noise cross-spectral density and coherence versus hydrophone separation installed inside the tube are calculated.
Energy losses in a boundary layer of an acoustical resonator
Authors: Ilinskii Yurii A. , Lipkens Bart , Zabolotskaya Evgenia A.
Published: July 2002

A one-dimensional model of nonlinear standing waves in an oscillating closed cavity has been developed and was presented at previous meetings. The present study focuses on an investigation of energy losses in the boundary layer and on the effect of the boundary layer on the acoustic field in the resonator. The boundary layer dissipation is much greater than the dissipation caused by volume attenuation. The fluid motion in the boundary layer is considered in a linear approximation. The boundary layer model is coupled with the one-dimensional model for the acoustics in the volume of the resonator. An interaction term which represents the flow from the boundary layer to the volume of the resonator is added to the mass conservation equation. A new modified one-dimensional equation that takes into account the flow from the boundary layer is obtained. Waveforms and harmonic amplitudes of pressure and velocity are calculated along the resonator axis with the modified model. The dissipation in the boundary layer and Q-factor of the resonator are also calculated. Results are presented for three geometries, i.e., a cone, a horn-cone, and a bulb.
Some characteristics of the self-induced sound-producing instabilities of under-expanded supersonic jets: Screech feedback
Authors: Powell Alan
Published: July 2002

The screech feedback loop differs from that of classical edgetones mainly in that: (a) the feedback is acoustic (vice hydrodynamic); (b) the source region (periodic stream disturbances interacting with the quasiperiodic spatial cell structure of the jet) is usually extensive, represented by a phased array of monopoles (vice a point dipole) with its ‘‘centroid’’ at h; (c) the feedback path length h between nozzle and effective source point, always crucial to the frequency, is strongly amplitude-dependent (vice given nozzle-edge distance) and presently inestimable; (d) the postulate of maximum amplitude in the nonlinear limit cycle implies self-adjustment, jointly, of amplitude and h, with the phased array emitting preferentially towards the nozzle, that emission tending to maximize and so yielding a good frequency estimate not based on h; (e) for round jets, the jet instability may be varicose, sinuous, or helical (vice just sinuous); for the helical jet instability (f) the acoustic feedback field must be correspondingly helical [Am. Inst. Aero. Astro. Paper 90-3980 (1990)], (g) the assumption of acoustic cutoff yields its cessation frequency, approximately; and (h) while the source mechanism remains controversial (vice an unambiguous force-dipole), a limiting amplitude is postulated for rectangular jets that also yields useful results.
Acoustic radiation pressure angular distributions and dependence on radius for the stabilization of liquid bridges in air and in immiscible liquids
Authors: Marston Philip L. , Thiessen David B. , Marr-Lyon Mark J.
Published: July 2002

Long liquid bridges are naturally unstable to the growth of an axisymmetric capillary mode. The active control of the axial distribution of the radiation pressure on density-matched oil bridges surrounded by water has been used to stabilize long bridges [M. J. Marr-Lyon et al., J. Fluid Mech. 351, 345–357 (1997)]. Bridges in air have been passively stabilized in low gravity [M. J. Marr-Lyon et al., submitted to this meeting] without active control by using the radial dependence of the angular average of the pressure [P. L. Marston, J. Acoust. Soc. Am. 97, 3377 (1995)]. The angular distribution of the radiation pressure affects the bridge response and was calculated and interpreted for cases of interest using the partial-wave series for circular cylinders. The tendency of bridges in air to flatten affects the choice of acoustic frequency for active control while the viscous dissipation of capillary modes is important for extending the integration time of the feedback. While ultrasound in the liquid bath was actively adjusted to expand the slender end of the bridge, calculations indicate that in air the fat end should be squeezed in order to reduce complications from flattening the bridge. [Work supported by NASA.]
A practical method for predicting ship machinery noise
Authors: Darby Ronald
Published: July 2002

The development of a ship’s noise prediction method at Annapolis from 1960 to 1967 is reviewed. In 1960, the Noise Transmission Branch was exploring mechanical impedance measurement concepts. Numerous structureborne and waterborne tests were made on machines, foundations, flexible couplings and conduits in the laboratory as well as on the SS427. The effort was complicated because of the large number of matrix elements describing even a simple machine foundation and the problems in obtaining meaningful measurements using the state-of-the-art instrumentation. The team’s ivy tower collapsed by urgent requests to predict radiated noise from a whole ship to assist BUSHIPS in decision making. A prediction model was developed using the force transfer factor concept by Wright and Akey. Based on in-house measurements and estimates from available literature, each transmission path component was categorized as a single spectrum. Vibration levels for each machine type were fed into representations of its transmission path components: isolation mounts, foundation, flanking paths (piping, conduits, etc.), and the hull. The team ended up with a practical prediction scheme to aid in the preliminary design stages of new ships and in guiding priorities for future research in ship silencing.
Supplementarity of damping and isolation and the invasion of humane aliens
Authors: Maidanik G.
Published: July 2002

The principle of supplementarity of damping and isolation states: When the inherent damping is increased in a driven structure that is coupled to a passive structure, the noise control benefit to the passive structure may not be as high as one may primitively predict. The coupling, in this case, may be in charge of the prevailing damping. On the other hand, when the driven and passive structures are merely isolated, this noise control effort may also not be effective. The increase in reverberation in the driven structure compensates, in part, for the increased isolation—reduced coupling. However, when both isolation and damping are instituted, the reverberation in the driven structure is controlled by the increase in damping and, then, the noise control in the passive structure is effective. The principle of supplementarity of damping and isolation is, thereby, explained. The relevance of this principle to the invasion of Earth by Humane Aliens will be narrated the way it was related, many years ago, to my colleagues at the Annapolis Lab.
Functions of the muscles of the tongue during speech
Authors: Kumada Masanobu , Todd Robert T. , Bell-Berti Fredericka , Niitsu Mamoru , Hirose Hajime , Niimi Seiji
Published: July 2002

To investigate the functions of tongue muscles during speech, three methods were combined: conventional MRI, to identify the musculature; tagging snapshot MRI, to visualize the displacement of tissues and measure contractions of muscles; and electromyography (EMG), to observe muscle activities. Five Tokyo-dialect speakers produced sustained phonations of five Japanese vowels. (Sessions of five English speakers are also planned to observe English vowels and consonants.) Muscle contractions of four regions of genioglossus (GG1-4, anterior to posterior), styloglossus (SG), vertical (V), superior and inferior longitudinal (SL, IL) were measured. The functional units of GG seemed to be overlapped with each other: GG3-4 to make the highest point of the tongue higher, working against V; GG2-4 to move the most posterior point anteriorly; and GG1-3 to move the highest point anteriorly, working against SG. SL contributed to groove formation. IL contributed to ‘‘landslide’’ formation in /o/ by keeping the lower half of the tongue forward against the posterior pull on the upper half by SG. EMG potentials from GG were higher in the supine than in the upright position, suggesting that there may be a system to generate different neural command patterns in relation to the direction of gravity. [Work supported by NIH DC-00865 to Haskins Laboratories, by St. John’s University, and by a Grant-in-Aid for Scientific Research (No. 01440071) from the Japanese Ministry of Education, Science, and Culture to the Department of Speech Physiology, Faculty of Medicine, University of Tokyo.]
The influence of large-scale seafloor slope and bottom velocity on low-grazing-angle monostatic acoustic reverberation
Authors: Greaves Robert J. , Stephen Ralph A.
Published: July 2002

Analysis of low-grazing-angle monostatic reverberation data acquired at Site A on the Acoustic Reverberation Special Research Program 1993 Acoustics Cruise suggests that scattered signals cannot be quantitatively explained in terms of large-scale slope alone, even though a strong correspondence between high intensity backscatter and seafloor ridges is observed. Numerical modeling using a finite-difference solution to the elastic wave equation shows that large-scale seafloor slope and subseafloor average velocity influence the backscattered intensity levels but that the source of scattering is wavelength-scale heterogeneity. The results of the modeling suggest that the influence of large-scale seafloor slope is strongest at small grazing angles. For example, for a rough seafloor and a source wave field incident at 15° relative to the horizontal, a change in the seafloor slope from 0° to 15° yields a 5-dB change in backscatter intensity, while a change from 15° to 30° in seafloor slope yields only a 1-dB change in backscatter intensity. The influence of average subseafloor velocity is shown to be a bimodal effect. Homogeneous soft bottoms, e.g., sediment, generate dramatically less backscatter than homogeneous hard bottoms, such as basalt.
Environmental factors for site-to-site differences in low-frequency surface scatter
Authors: Hanson Jeffrey L.
Published: July 2002

Acoustic reverberation experiments conducted during the extensive Critical Sea Test (CST) Program have indicated that near-surface microbubble clouds are the primary source of low-frequency (0–1000 Hz) acoustic surface scatter during elevated winds. A crucial issue remaining from CST, however, is the explanation of large (greater than 15 dB) site-to-site differences in surface scattering strength. Using the extensive CST environmental observation set, as well as satellite remote sensing products available over the World Wide Web, we have investigated the hypothesis that site-to-site differences are controlled by processes related to the supply, mixing, and removal of near-surface bubbles in the ocean. It is found that much of the variability can be empirically explained by considering the mean ocean temperature, biological productivity, and wave conditions at each site. These results provide important clues as to the controlling factors for surface scatter in shallow water areas, where biological productivity is highest. The implications for improving an operational surface scattering prediction capability, using readily available (e.g., satellite observations) environmental inputs, will be discussed. [Work supported by the Office of Naval Research/Ocean Acoustics.]
Flexible acoustics for two purpose-built organ recital halls
Authors: Kahn David
Published: July 2002

It is rare today for any purpose-built music performance spaces to be commissioned, be they opera houses, concert halls, organ recital halls, etc. In order for any performance venue to be truly successful today, it must have flexibility included in its design, allowing the space to function well for the wide range of performance types that will inevitably be scheduled. The same can be said for purpose-built pipe-organ recital halls. While the highest design priority might be organ music, all but the most esoteric of these rooms will also be required to support far more than pipe-organ music. This paper will discuss two ‘‘purpose-built’’ pipe-organ recital halls with flexible acoustics devices which allow these spaces to function well for uses other than pipe-organ recitals. North Hall at the Peabody Conservatory at Johns Hopkins University in Baltimore, MD, is now used primarily as a pipe-organ recital hall for a new Holtkamp tracker organ. This hall also continues to function as a rehearsal room for large ensembles. The University of Northern Iowa is building a multi-purpose 125-seat organ recital hall and choral rehearsal room. This hybrid space uses additional partially coupled volumes to better support a new Hellmuth Wolff tracker organ.
Biological high-frequency ambient noise
Authors: Macaulay Michael C.
Published: July 2002

Biological sources of ambient noise have long been known to be produced by many invertebrates, fish, and marine mammals. Investigations have identified, specifically, many causative organisms that produce noise levels well in excess of those produced by purely physical phenomena (e.g., wind, wave activity, rain, etc.). The noise level produced by many of these sources can be as intense as many electronic systems (i.e., greater than 200 dB at 1 m // 1 μPa). In other cases, it interferes with our ability to utilize high-frequency acoustic signals for detection of objects or for measuring environmental sources of noise. This presentation will examine some of the known sources of biological ambient noise in relation to noise levels of nonbiological origin, whether known sources can be used as representative less well-known sources, and possible sources of error in the determination of signal characteristics. The primary purpose of this presentation is to place boundary conditions on the extent of our present knowledge, suggest guidelines for improving our understanding of their possible impact, and to point out where our information may be deficient.
Optimal performance of thermoacoustic coolers with spring–mass and electrodynamic driver resonator configurations
Authors: Minner B. L. , Savran C. , Mongeau L. , Braun J. E.
Published: July 2002

Acoustic resonators are often used on the cold side of thermoacoustic coolers in order to maintain the proper phasing between fluid particle displacement, pressure, and temperature within the stack. These devices tend to occupy a large volume, which is a potential disadvantage for applications where space is at a premium. In the present study, two alternative cold side resonator configurations were evaluated: (1) a spring–mass system; and (2) an electrodynamic driver. The inverse problem of determining the system parameters required in order to operate the system at resonance for given compression ratios, complex pressure phase gradients, operating frequency, and load impedance was solved. The optimal efficiency of the alternative resonator systems was calculated and compared with that of a system with an acoustical resonator configuration. For this, previously reported robust optimal design methodologies were used [Minner et al., J. Acoust. Soc. Am. 98, 2961 (1995)]. The benefits and disadvantages of each resonator configuration will be discussed.
Review and status of sonic boom noise penetration into the ocean
Authors: Sparrow Victor W.
Published: July 2002

Since the 1970 Sonic Boom Symposium, held at the ASA’s 80th meeting in Houston, TX, substantial progress has been made in understanding the penetration of sonic boom noise into the ocean. The state of the art at that time was documented by J. C. Cook, T. Goforth, and R. K. Cook [J. Acoust. Soc. Am. 51, 729–741 (1972)]. Since then, additional experiments have been performed which corroborate R. K. Cook’s and K. Sawyers’ theory for sonic boom penetration into a flat ocean surface. In addition, computational simulations have validated that theory and extended the work to include arbitrarily shaped waveforms penetrating flat ocean surfaces. Further numerical studies have investigated realistic ocean surfaces including both large-scale ocean swell and small-scale surface roughness. Research has also been performed on the effects of ocean inhomogeneities due to bubble plumes. This paper will provide a brief overview of these developments.
Sonic boom noise penetration under a wavy ocean
Authors: Cheng H. K. , Lee C. J.
Published: July 2002

Interaction of incident sonic boom waves with a wavy ocean can profoundly influence their underwater noise propagation and affect the perceived sound-pressure level far more significantly than anticipated from the flat-ocean (Sawyer) model. The theory assumes a small departure (in surface slope) from a flat ocean; the study takes into consideration the extremely high water-to-air density ratio, and the sound speed being higher in water than in air. The analysis treats the time-dependent interaction with a sinusoidal surface wave train, addressing primarily the case in which the wave-field Mach number is subsonic underwater. Two distinct wave components, identifiable via the stationary-phase principle, emerge in the sound field far below the surface. The reinforcing mechanism implicit in the stationary phase leads to a greatly reduced signal attenuation rate, and renders the waviness influence an effect of the first-order importance at large depth. Dominant frequencies and sound-pressure levels computed at various depths for the model of a fully developed sea state are compared to available data of underwater sound characteristics pertaining to baleen whales. Pronounced sea-floor effects and the significant differences between space launch and aircraft sonic boom noise underwater are noted.
Inversion of seabed porosity and permeability using pore pressure probe data
Authors: Mu Yongke , Badiey Mohsen , Cheng Alexander H.-D. , Liu Zhong , Bennett Richard H.
Published: July 2002

In shallow water acoustics two very important physical parameters affecting the acoustic wave dissipation are porosity and permeability. These properties are better obtained in situ than in the laboratory. To avoid large-scale acoustic experiment and an inversion that provides only the range averaged properties, the in situ pore pressure measurement by probes on and in the surfacial sediments could be used. The probe penetrates the seabed and measures the seabed pore pressure response to water waves. To use the data to invert for porosity and permeability, the analytical solution of the forward problem based on the Biot theory of poroelasticity is first constructed. Sensitivity analysis is conducted with respect to the porosity and the degree of saturation. Considering the empirical relationships between physical parameters, a minimum set of data required for predicting the pore pressure is presented. The inversion is applied to the field measured data and the results are compared with the independent measurements of these parameters.
Fourier transformation for nondestructive evaluation
Authors: Dayal Vinay
Published: July 2002

Fourier transformation of the time domain signal has been used for a variety of applications in the area of nondestructive evaluation of both isotropic and composite materials. Reflection pulses, which are close together in time domain, can be separated out in the frequency domain. The information from the reflected or refracted pulses was deconvolved and the wave velocity/sample thickness and damping for very thin samples could be measured [V. K. Kinra and V. Dayal, Exp. Mech. 28(3), 288–297 (1988)]. The added advantage of these techniques is that they immediately warn the user of the dispersion in the material. Fourier transform of pulses was applied to the measurement of the wave velocity of Lamb waves. Lamb waves or plate waves are affected by the in-plane material properties and, for platelike structures, this measurement is very useful in making velocity and damping measurements [V. Dayal, Rev. Prog. QNDE 13A, 189–194]. The technique has since been used for the measurements of mechanical properties such as elastic constants of composite materials, automated simultaneous measurement of wave speed and thickness, and measurement of very thin coatings. Various applications will be reviewed.
Improvements on the design of the electrodynamic transducer coils used in spectropic determination of acoustic constants of thin bars
Authors: Guo Qiushuang , Brown David A.
Published: July 2002

The resonant bar technique for measuring the acoustic properties of materials is inexpensive, easy to perform, and has the advantage of high signal-to-noise ratio. The design of transducer coils used to selectively excite and detect bar motion is crucial to obtain good data. A new electrodynamic transducer design is presented. The new transducers are small in size and mass and glued at the ends of the bar so that perturbations due to the transducers are small and easy to model. This design is more selective and permits less mechanical cross talk among longitudinal, flexural, and torsional modes. It also has negligible electrical cross talk between transducers. [Work supported by the Ph.D. Program and the STrategic Envirotechnology Partnership (STEP) through the Advanced Technology Center at the University of Massachusetts Dartmouth.]
Propagation of transient ultrasound in a thick annulus: Modeling, experiments, and application to crack detection
Authors: Li Zongbao , Berthelot Yves H.
Published: July 2002

Fatigue cracks often develop on the inner surface of annular components such as collars. Ultrasonic guided wave propagation can be used for nondestructive evaluation of such structures. A wave mode expansion solution is formulated for transient excitation of circumferential waves at the outer surface of a thick annulus by a distributed traction source (modeling a piezoelectric source with an angular wedge). The solution provides valuable information on the energy distribution inside the annulus and the modal content of the detected signals. The predicted waveforms are compared with experimental results obtained with a 2.25-MHz transducer for various wedge angles, and for various positions of the receiver on the outer surface. Crack detection in the annulus is investigated with transient circumferential waves. It is shown that a 1-mm machine-made radial crack on the inner surface can be detected. [Work supported by the ONR under a M-URI Center for Integrated Diagnostics.]
Acoustical characteristics of leak sounds in plastic pipes
Authors: Chu Wing T. , Hunaidi Osama
Published: July 2002

As an integral part of the AWWARF/NRC research project on the evaluation of existing methods for pinpointing leaks in plastic pipes, the acoustical characteristics of leak sounds in plastic pipes have been studied at the NRC’s PVC pipe experimental leak detection simulator under controlled conditions. Tests have been performed both in the summer and in the winter. Experimental techniques and test results on the frequency content, attenuation rate, and propagation velocity will be presented in this paper.
Acoustical phase locking
Authors: Keolian Robert M.
Published: July 2002

A self-maintained oscillator, such as a beating heart, influenced by another oscillator, such as a pacemaker, may adjust its frequency so that the phase between the two oscillators is constant, thus making their frequencies identical. In general, the two oscillators will synchronize if the coupling between them is strong enough and their natural frequencies are close enough. This phase locking or entrainment phenomenon is fairly common. Two clocks on the same wall can force each other to tick in unison, the moon shows us only one face because its spin and orbital frequencies are locked, two people walking together often unconsciously adjust their pace until their feet hit the ground simultaneously, and our sleep–wake cycle or the laying of chicken eggs is synchronized with the rotations of the earth. Here, phase locking will be demonstrated with a slide whistle influenced by a nearby loudspeaker.
The air-conditioning and refrigeration institute sound labeling program—Past, present, and future challenges
Authors: Comparin Robert J.
Published: July 2002

In the late 1960s, ARI developed a voluntary sound labeling program for air-cooled condensing units. The program was in response to consumer complaints of excessive noise. A major part of the problem was prominent discrete frequency components. The sound label was based on an overall, A-weighted, sound power level that was adjusted by adding a penalty when prominent discrete frequency components were present. Sound labels were published in an ARI equipment directory and were subject to verification by an independent testing laboratory. Initially, there were a large number of participants in the program and the program resulted in a reduction in overall equipment noise levels including the discrete frequency components. Surprisingly, the introduction of new products with a greater emphasis on lower noise levels has actually led to a reduction in the number of manufacturers participating in the program. This was due to concerns that the discrete frequency penalty adjustment no longer adequately reflected annoyance. ARI is currently working to improving the adjustment for discrete frequency components. The presentation summarizes the history of the ARI sound rating program and examines some of the practical problems associated with the development and maintenance of the program.
Product labeling and sound quality
Authors: Davies Patricia
Published: July 2002

Sound power and dB(A) ratings of commercial products may be deceiving when the consumer is trying to make some judgement as to the pleasantness of the product sound. The quality of the sound is affected by tonal content, tonal relationships, variations in level and spectral balance, in addition to the overall average level of the product sound. Even different level metrics, e.g., A-weighted SPL, and Zwicker Loudness, may give contradictory indications as to which product is quieter. In addition, tuning the product to have a lower metric value may lead to a product that sounds worse, if the key characteristics of that product sound are not taken into consideration in the metric. One approach to rating is to have people rate the product sounds, but if these subjective tests are not carried out in a prescribed and rigorous manner, the results may be meaningless. Ordering effects in sound presentation, inconsistent measurements and the use of nonsound-related product information could lead to poor product sound comparisons. The presentation will be focused on the issues involved in quantifying sound quality for product labeling.