bluuebunny/crossref_metadata_2025 huggingface dataset:
Multiple scattering in marine sediments with volume inhomogeneities
Authors: Ivakin Anatoliy N.
Published: July 2002

Scattering by sediment inhomogeneities is recognized as one of major contributors to sea bed scattering and reverberation. In practical modeling, various single-scattering assumptions are normally used. While these assumptions may be reasonable in many cases, it is usually untested. Here, it is shown that conditions of validity for conventional single-scattering approximations can fail at realistic values of sediment parameters. In particular, the field can be strongly fluctuating and randomized in significant part of insonofied sediment volume, which is in essential contradiction with the main assumption of single-scattering theories. In certain cases, this difficulty can be overcome in the frame of the so-called cumulative forward-scatter single back-scatter (CFSB) approximation developed for the problem of wave scattering in the atmosphere [de Wolf, 1971]. Examples of application of this theory to sea bed scattering are presented and multiple scattering effects are considered. Also, problems specific for seabed scattering are discussed which arise due to the greater strength of nonforward scattering by strong fluctuations of the density, the proximity of the water-sediment interface, at small grazing angles and near the critical angle. [Work supported by ONR.]
Optimal absorption surface in offices and conference rooms
Authors: Picard Lopez M. A. , Solana Quiros P. E. , Arizo Serrula J. V.
Published: July 2002

In the process of acoustic conditioning of enclosures it is necessary to follow an iterative process in order to obtain the suitable reverberation times (RTs) in the different frequencies, as a function of the use of the enclosure. In order to attain accurate results, it is necessary to modify adequately the absorption characteristics of the internal surfaces of the enclosure and other devices that would have to be included in it. To simplify the calculation process, an inverse process can be used. Noting the desirable reverberation times, optimal absorption surfaces can be obtained. In this way, the most adequate materials and coatings can be selected from a database. From numerous studies and works related to the topic, the optimal reverberation times are determined for the type of enclosures mentioned. From this study, the optimal absorption surfaces can be obtained, which lead to the reverberation times already mentioned. In this work are supplied the graphics and functions in octave bands of the optimal absorption surface as a function of volume; the absorption average coefficient value of enclosure; the value of the constant optimum of the enclosure (R); and the optimum reduction coefficient of noise (NRC).
Pulse propagation of acoustic waves scattered in a three-dimensional channel
Authors: Whitman Alan M. , Beran Mark J.
Published: July 2002

In a previous paper [A. M. Whitman and M. J. Beran, Waves in Random Media 11, 1–11 (1999)] we discussed the scattering of acoustic waves by random sound-speed fluctuations in a two-dimensional channel and presented an asymptotic form for an acoustic pulse propagating in the channel. Here we include the three-dimensional effect of transverse scattering. We find an asymptotic solution in which initially the two-dimensional mode-transfer effect is more important than the transverse scattering effect. However, for large enough propagation distances the transverse scattering dominates the pulse spread. Here we show the form of the pulse shape in both propagation ranges as well as the transition regime. We begin with a discussion of the physics of the problem and then present a mathematical discussion.
A one-way coupled mode solution, Huygens’ principle and mode coupling coefficients
Authors: Werby Michael F.
Published: July 2002

The normal mode formulation for waveguide propagation has physical appeal since sound propagates in discrete entities—namely modes—and an understanding of the progression of modes sheds light on arrival times of pulses and features of ocean ducting. In the development of the range-dependent version several researchers employ the conservation of normal pressure and normal particle velocity along the z axis in the mean as the conserved quantity that allows for an algorithm to couple the modes as sound progresses in range. The usual derivations are based on R. Evan’s seminal work on the two-way coupled mode formulation. Here it is shown that Huygens’ principle and an approximate form of the Green’s function in the waveguide leads to a suitable algorithm as long as reflected or backward going flux is small relative to forward flux. The derivation, moreover, leads to expressions for mode coupling amplitudes that allow one to follow the distribution of flux along specific modal tracts. [Work supported by the Office of Naval Research and Naval Research Laboratory.]
Influence of beam geometry and tissue boundaries on thermal ultrasonic lesions
Authors: Lizzi Frederic L.
Published: July 2002

The size and shape of thermal lesions induced by high-intensity focused ultrasound (HIFU) are key factors in treating disease. Studies are being conducted to determine how HIFU beams and exposures can be designed to produce useful lesion attributes in specific target tissues. The studies include radially asymmetric beams and tissues with different acoustic absorption coefficients; sharp thermal gradients at such boundaries can significantly affect lesion geometry. Ocular tumor therapy uses asymmetric beams that produce lesions with ellipsoidal cross sections to facilitate treatments with closely packed lesion matrices. Three-dimensional simulations have analyzed heat patterns and lesions induced by these beams in irregular tumors whose geometry is derived from clinical serial-plane scans using 50-MHz diagnostic ultrasound. The simulations documented difficulties in treating boundary regions adjacent to the waterlike vitreous humor. Lesion results were consistent with in vitro and in vivo animal experiments. A related study involves an annular-array therapy system with a central rectangular aperture, housing a diagnostic array. The system (Spectrasonics, Inc.) is intended for treatments in various organs, including liver. Since the therapy beams are not radially symmetric, 3-D simulations and initial animal experiments have examined the asymmetry in induced temperature patterns and lesions. These investigations also addressed spurious grating peaks in axial intensity.
Self-focusing ultrasound phased arrays for noninvasive surgery
Authors: Ebbini Emad S.
Published: July 2002

Modern transducer technology is providing phased arrays with high-power, relatively large fractional bandwidth, and low cross coupling between array elements. As a result, it is possible to use these arrays in a dual imaging/therapy mode. We have recently demonstrated this using a 64-element 1-MHz array with 1.5×50 mm2 elements on a spherical shell with a 100-mm radius of curvature. In the therapy mode, the array was shown to be capable of producing focal intensities in excess of 10000 W/cm2 and cause well-defined lesions in tissue at depth. In the imaging mode, the array was shown to be capable of forming images of acceptable quality in a region covering ±35 mm axially and ±25 mm laterally around its geometric center. In this paper, we describe new algorithms for using this array in self-focusing mode based on acoustic feedback from the intended focal region. Two modes of acoustic feedback will be described and compared, specifically, direct hydrophone measurements at the desired focus and backscatter from the focal region (collected in imaging mode). Experimental data are given to demonstrate optimal focusing of phased array systems in the presence of strongly scattering objects, e.g., the ribcage.
Ultrasound-induced enhancement of skin permeability to Octa-L-Lysine
Authors: Weimann Ludwig J. , Wu Junru
Published: July 2002

The efficiency of ultrasound in transdermal delivery of high molecular weight protein drugs has been demonstrated recently [S. Mitragotri et al., Science 269, 850–853 (1995)]. It has been shown in our previous paper [J. Wu et al., Ultrasound Med. Biol. 24, 1–6 (1998)] that ultrasound-induced structural disorder in human stratum corneum may be responsible for the enhancement of skin permeability. In this presentation, the effect of 20-kHz ultrasound on the permeation of Octa-L-Lysine tagged with Fluorescein (Octa-L-Lysine-4-FITC, effective molecular weight 2.5 kDa) through the skin was shown by optical reflection images and confocal microscopic cross-sectional images of skin. It has been indicated that both sonophoresis and sonoporation may be involved in the procedure. The possible mechanisms and bioeffects introduced by the procedure will also be discussed.
Fault detection in engines through higher order spectral analysis of acoustic signatures
Authors: Meegan G. D. , Nelson H. R. , Barlett M. , Wilson G. R.
Published: July 2002

This paper describes new engine fault detection methods that involve a higher order spectral analysis method known as the parametric spectral coherence (PSC). Measurements of radiated acoustic and vibrational signatures were conducted on a one-cylinder engine with a continuously worsening loss of cylinder compression. Compared to vibrational signatures, the radiated acoustic signatures provided the most dramatic indication of a loss of cylinder compression when PSC analysis was performed. It is demonstrated that the fault can be detected by simply monitoring the average spectral coherence or the peak spectral coherence of the acoustic signature, whereas the more traditional power spectral methods fail to detect the fault.
Path-integrated Goldberg number as a predictor of enhanced heating from finite-amplitude therapeutic ultrasound sources
Authors: Hallaj Ibrahim M. , Hynynen Kullervo , Cleveland Robin O.
Published: July 2002

Several theoretical and experimental studies have demonstrated that the higher-frequency harmonics generated by finite-amplitude propagation from therapeutic ultrasound sources result in enhanced heating of tissue. However, published results vary in their assessments of the significance of the nonlinearity on tissue heating. The variations in the results are due to the use of different sources and propagation paths. It would be useful to have an easily computed estimator of finite-amplitude effects for therapeutic ultrasound sources. The present study describes a dimensionless quantity, which takes the propagation path into account, to estimate the excess temperature rise due to nonlinearity. The dimensionless parameter is based on the Goldberg number which is a measure of the importance of nonlinear effects to absorption effects. The relationship between the enhanced heating of tissue and the path-integrated Goldberg number for water-tissue paths is presented for typical therapeutic devices. [Work sponsored by National Cancer Institute.]
A novel dual-band equalizer design for loudspeaker systems
Authors: Wang Peng , Ser Wee , Zhang Ming
Published: July 2002

Many equalization methods based on DSP technology have been proposed during the past decade. However, nearly all the methods demand low-frequency components to be processed separately because of deficient resolution. A dual-band equalization method for loudspeaker systems is presented in this paper. In this method, the conventional equalization based on deconvolution of the system response and a recently introduced method based on warped filter design are combined, to achieve a refined performance in the whole audio frequency region with lower order filter. Computer simulations are given to demonstrate the effectiveness.
Calibration or conformance check. What is the difference
Authors: Schonthal Ernst
Published: July 2002

Both measurements are performed using certified equipment. A certificate is issued after both measurements. This paper will address the difference between the two certificates and why calibration is important. Also this paper will explain some instances where one has to do both.
Simulating meter perception in acoustic signals
Authors: Large Edward W.
Published: July 2002

A model of meter perception is presented in which an acoustic signal provides parametric input to a pattern-forming dynamical system. Under rhythmic stimulation, the system undergoes bifurcations that give rise to patterns of self-sustained oscillations. The temporal structure of these patterns reflects the perceived temporal organization of acoustic signals that has been described by both linguists and music theorists [M. Liberman and A. M. Prince, Ling. Inq. 8, 249–336 (1977); F. Lerdahl and R. Jackendoff, Generative Theory of Tonal Music (MIT, Cambridge, 1983)]. These patterns are stable, yet flexible: They can persist in the absence of input and in the face of conflict, yet they can reorganize given a strong indication of a new temporal structure. Both continuous and discrete time models will be discussed and their application to acoustic signals will be demonstrated.
Motor learning, meter, and rhythm in music performance
Authors: Meyer Rosalee K.
Published: July 2002

What do musicians learn when they perform music: motor-independent knowledge specifying abstract concepts or motor-specific knowledge designating motor movements? Whereas some theories of se- quence production suggest that timing is motor independent, others have suggested a closer relationship between timing and motor movements. Previous research suggests that skilled pianists’ knowledge of how to perform simple melodies is motor independent [C. Palmer and R. K. Meyer, Psychol. Sci. (in press)]. However, the relationship of motor movements to temporal structures such as meter (periodic accent structure) and rhythm (duration pattern) were not addressed in this study. Two experiments reported here investigate whether skilled pianists’ knowledge of meter and rhythm is motor independent or motor specific. In a transfer of learning paradigm, pianists performed a short musical piece under speeded conditions and then transferred to another musical piece with identical pitches but the same or different motor movements. In experiment 1, the transfer melody contained the same or different meter, and in experiment 2, the transfer melody contained the same or different rhythm. Changes in total sequence duration indicate the importance of motor-specific knowledge in the context of music that differs in temporal dimensions such as meter and rhythm. [Work supported by NIMH.]
Local ordinance targeted to low-frequency noise
Authors: Brooks Bennett
Published: July 2002

The local authorities of a suburban town wanted to control the low-frequency noise emissions due to musical entertainment at night clubs and taverns. Complaints from residents about booming bass guitar and drum sounds had to be balanced with the need for tavern owners to reasonably conduct business. It was recognized that the existing town code, which placed limits on A-weighted noise levels at property boundaries, was not an effective means to control low-frequency noise emissions. A revised ordinance was developed to address this issue, which now places additional limits on the allowable noise levels in specific octave bands. In particular, this includes the low-frequency (bass) octave bands. The octave band limits were selected such that the summation of band levels equals the A-weighted overall noise limit.
CNEL at two sites in Del Mar, due to a hundred helicopter flybys
Authors: Young Robert W.
Published: July 2002

In the Settlement Agreement in early 1999 of a lawsuit about helicopter noise, in which the City of Del Mar was one of the plaintiffs and the Marine Corps was one of the Federal defendants, there was a requirement that the community noise equivalent level (CNEL) be included as a standard for measuring noise significance. This is a preliminary report about CNEL measured continually at two sites in south Del Mar, California. In both cases the residents had filed official complaints about the noise of helicopters. These residences are distance from heavily traveled streets and highways. The automatic noise monitor consists of a Computer Engineering, Ltd., 493-2 integrating sound-level meter feeding a CEL-238 secondary processor, all in a weather-proof case. The outfit prints, and puts in memory, the one-hour average sound level during a preceding hour and at the end of a day the 24-hour average sound level (24 HL), the day–night average sound level (DNL), and the CNEL. At 22839 Via Grimaldi, Friday to Wednesday 5–10 May 99, the CNELs were 55.8, 55.5, 54.6, 55.9, 58.7, and 58.7 dB. At 421 Ocean Drive, Tuesday to Saturday 11–15 May 99, the CNELs were 58.4, 56.5, 59.6, 58.6, and 60.5 dB.
Noise dosimetry for telephone users
Authors: Moquin Philippe
Published: July 2002

Due to recent F.C.C. regulations, all telephones in North America will be required to have at least 12 dB of amplification. While this is a definite asset to the hard of hearing community, there are fears that normal hearing workers who use the telephone most of the day could suffer noise-induced hearing loss. Theoretical calculations validate this hypothesis. Measurements of actual levels in a call center were taken. Finally, a method of providing noise dosimetry within a digital telephone set is presented. Simultaneous measurements show good correlation.
Thermal performance of heat exchangers for thermoacoustic refrigerators
Authors: Chen Yuwen , Herman Cila
Published: July 2002

Heat exchangers in thermoacoustic refrigerators extract heat from the refrigerated volume and reject it to the surroundings. Eight essential heat-transfer processes coupled in the energy migration from the cold-side heat exchanger through the stack to the hot-side heat exchanger were identified, and a simplified computational model describing them was developed. Geometrical and operational parameters as well as thermophysical properties of the heat exchangners, the stack plate, and the working medium were organized into dimensionless groups. Heat transfer in the transverse direction, resulting from temperature differences between the inlet and outlet temperatures of the transport fluid in the heat exchangers, was accounted for in the simulations. Two types of boundary conditions between the thermoacoustic working fluid and the heat exchangers were considered: (1) constant temperature of the thermoacoustic working fluid over the heat exchangers with constant temperature difference along and across the stack and (2) constant heat flux from the thermoacoustic working fluid to the heat exchanger. Nonlinear temperature distributions and heat fluxes near the edge of the stack plate were observed. Effects of different parameters on the thermal performance of the heat exchangers were investigated. [Work supported by the Office of Naval Research.]
Use of electrodynamic drivers in thermoacoustic refrigerators
Authors: Wakeland Ray Scott
Published: July 2002

Some issues involved in matching electrodynamic drivers to thermoacoustic refrigerators are examined using an equivalent circuit model. Conclusions are that the driver should be chosen to have a large product (Bl)2/(ReRm). The suspension stiffness should be chosen to make the combined impedance of the mechanical and acoustical parts of the system entirely real at the operating frequency. The piston area should be selected to maximize electroacoustic efficiency or other desired parameters by matching the acoustical load to the optimum mechanical load for the particular driver. Alternately, if the piston area is fixed, the operating frequency can be adjusted to make this same match. Measurements made at this laboratory [R. W. M. Smith et al., J. Acoust. Soc. Am. 105, 1072(A) (1999)] provide experimental support for the conclusions of this paper concerning the attainable maximum electroacoustic efficiency. [Work supported by NSF and ONR.]
Streaming in thermoacoustic engines
Authors: Smith Gordon , Raspet Richard , Bass Henry
Published: July 2002

Thermoacoustics utilizes an acoustic process to transport heat. Interestingly enough, sound sources that move essentially in a sinusoidal manner often do not yield flow fields of a sinusoidal nature. In addition to the oscillation of each fluid element contributing to the acoustic system, there can exist a pattern of steady vortices or other time-independent circulation regions known as acoustic streaming. Many different models for acoustic streaming have been developed, each stemming from a unique specific premise to the problem. Within a thermoacoustic device, acoustic streaming provides a means for a thermal short, in which a direct fluid flow would be established between two heat exchangers, permitting a much easier path for thermal transport than that established by a thermoacoustic process. However, little empirical data exist to provide a means of estimating the amount of thermal loss from such a process. Theoretical work to date will be presented, as well as experimental data from a single stage prime-mover thermoacoustic device. [Work supported by ONR.]
Pitch of envelope-modulated rippled noise
Authors: Sheft Stanley , Yost William A.
Published: July 2002

Both amplitude modulation (AM) and the delay-and-add process of rippled-noise (RN) generation can impart a pitch to wideband Gaussian noise. For AM, and possibly also RN, the basis of the pitch percept derives from temporal processing of the stimulus. In the present study, the pitch of envelope-modulated rippled noise was matched to filtered pulse trains. RN was generated with a delay of either 5 or 10 ms with either one or eight iterations and a gain of either plus or minus one. AM rates ranged from 50 to 200 Hz. Without rippling the carrier, accuracy in pitch matching to AM rate was fairly consistent over the range of rates studied with most deviations occurring as ‘‘octave errors.’’ With envelope modulation of RN carriers, pitch matches were distributed between pitches associated with the AM rate and fine-structure delay, in some cases with a noticeable increase in ‘‘octave errors.’’ Even with eight iterations in RN generation, an influence of AM rate on pitch matches was obtained. Pitch-match distributions can be roughly accounted for by consideration of the largest positive peak of both the fine-structure and envelope autocorrelation functions. [Work supported by NIH and AFOSR.]
Structural intensity in a point-excited infinite elastic plate in the high-frequency range
Authors: Hayek Sabih I. , Won Jungyun
Published: July 2002

An infinite elastic plate is excited by a mechanical point force, which generates a vector active structural intensity field in the plate. In an earlier paper [Hayek et al., J. Acoust. Soc. Am. 105, 1299 (1999)], the structural intensity was evaluated analytically for a plate using the Bernoulli–Euler theory, which is valid in the low-frequency range. The paper then employed the same theory for the active control of total structural intensity by use of co-located point forces and moments. In this paper, the evaluation of the vector structural intensity field due to point forces and moments is modeled by use of the more exact Mindlin plate theory, which is valid in a much higher frequency range. The main objective is to achieve active control of the total structural intensity in infinite elastic plates using the Mindlin plate theory through a co-located point force and a point moment actuator at an arbitrary location on the plate.
Transverse wave motion of piezoelectric (622) layer due to step potential
Authors: Anandam C. , Natrajan R. , Paul H. S.
Published: July 2002

The propagation of transverse waves in a piezoelectric layer of class (622) is investigated, when excited by either (a) step electric potential, keeping zero stress or (b) step shear stress, keeping zero potential. The resulting electric potential or shear stress is presented graphically. For case (a), electric potential linearly increases as the thickness of the plate increases, whereas stress is maximum near nondimensional thickness r=0.1 and decreases gradually and becomes zero at the top surface. For case (b), electric potential becomes negative and linearly decreases up to nondimensional thickness, r=0.87 and then increases and becomes zero at the top surface with slight oscillatory nature as the thickness of the plate increases. It is also observed that mere application of time dependent electric potential in piezoelectric (622) class generates transverse waves, which is not possible in any other piezoelectric material.
Audibility and visual biasing in speech perception
Authors: Clement Bart R. , Carney Arlene E.
Published: July 2002

Evidence of an integrative interaction between vision and audition comes from studies of audiovisual disparity, in which conflicting auditory and visual speech tokens may elicit a fused perceptual response that is different from that represented in either modality alone (i.e., the ‘‘McGurk Effect’’). Visual information in speech can bias and in some cases even dominate the auditory percept. Hearing-impaired listeners may be more susceptible to visual biasing in speech perception than normal-hearing listeners because of an increased reliance on visual information. It is argued here that the degree of audibility of the auditory component of the stimulus must be equated across the two groups before true differences in visual biasing can be established. In the current investigation, the effects of visual biasing on speech perception are examined as audibility is systematically degraded for 12 normal-hearing listeners and two male talkers. Results demonstrate that the degree of visual biasing is in fact related to degree of audibility. Further, individual normal-hearing listeners may differ distinctly with regard to how they integrate the two modes of information. Both of these factors must be considered when this phenomenon is studied in hearing-impaired listeners. [Research supported by NIDCD.]
Testing the relative salience of audio and visual cues for stop place of articulation
Authors: Winters Stephen J.
Published: July 2002

Recent OT analyses have appealed to putatively universal rankings of perceptual entities in order to motivate analyses of phonological phenomena. J. Jun [WCCFL 14, 221–237 (1995)] bases a universal constraint ranking for susceptibility of stops to place assimilation on the inherent ‘‘salience’’ of place cues. E. Hume [WCCFL 17 (1998)] appeals to the ‘‘perceptual vulnerability’’ of labial stops in order to account for their cross-linguistic tendency to undergo metathesis. Both phonologists motivate their analyses with speculative and unquantified assumptions about place cue salience. This study used an objective definition of salience to empirically establish the relative strengths of audio and visual cues for stop place of articulation. Comparing results between audio-visual and audio-only groups showed that visual cues are strongest for labials but are also significantly higher for coronals than dorsals. Adding acoustic information between speech reception threshold and comfortable listening level conditions had weaker effects than adding visual information, but contributed most strongly to the intelligibility of dorsals. Overall results suggested that labial stops have the strongest cues for place regardless of modality, contrary to what Hume, Jun and other researchers would predict. [This material is based upon work supported by a National Science Foundation Graduate Fellowship.]
Auditory-visual integration in younger and older adults
Authors: Sommers Mitchell S. , Tye-Murray Nancy
Published: July 2002

This study examined age-related changes in the ability to integrate auditory and visual speech information. Visual enhancement, the advantage afforded by seeing as well as hearing a talker, compared with listening alone, was measured in younger (18–25) and older (over age 65) adults. In addition, dichotic identification of filtered speech (auditory–auditory speech integration) and binaural gap detection (auditory–auditory nonspeech integration) were tested to evaluate whether auditory-visual integration was related to a more global ability to integrate sensory signals, be they speech or nonspeech. Visual enhancement was significantly impaired in older, compared with younger adults. Importantly, visual-only (lipreading) performance of younger and older adults was nearly identical, suggesting that age-related declines in visual enhancement were not a result of reduced reception of visual information. Older adults also exhibited deficits in the ability to integrate two channels of auditory information and these deficits were similar for both speech (sentences) and nonspeech (gap detection) stimuli. Regression analyses indicated significant correlations between the three measures of sensory integration, visual enhancement, dichotic sentence identification, and binaural gap detection. Taken together, the findings suggest that age-related declines in visual enhancement are a result of a generalized decline in sensory integration abilities.
Geometrical displays of speech spectra as aids to lipreading
Authors: Tait Steven L. , Strong William J.
Published: July 2002

Many syllables are ambiguous to lip readers because of their similar appearance on the lips. An aid is necessary to make distinction of these syllables possible. In a previous study [E. J. Hunter and W. J. Strong, J. Acoust. Soc. Am. 102, 3166–3167 (1997)], speech spectra were processed at 5-ms intervals and displayed as sequences of irregular decagons. Subjects were asked to discriminate between pairs of decagons representing ambiguous syllables. Subjects successfully discriminated most pairs, but were inconsistent in discrimination of voiced-/unvoiced-stop pairs. This study is concerned with display formats aimed at improving discrimination of ambiguous pairs to develop a more effective aid for lip readers. In particular, ‘‘pie slice’’ and ray formats are evaluated against polygons. Filled shapes are evaluated against open shapes. Five-band speech spectra are evaluated against ten-band spectra. Display color is evaluated against line thickness for representing overall sound level.
Prosodic disambiguation of syntactic ambiguity in discourse context
Authors: Speer Shari R. , Sokol Shari B. , Schafer Amy J. , Warren Paul
Published: July 2002

A cooperative boardgame task was used to examine how native speakers use prosodic structure to resolve syntactic ambiguity in discourse context. The game task required two speakers to use utterances from a predetermined set to negotiate the movement of gamepieces to goal locations. In one condition, the discourse contained two situations that had to be described using the same syntactically ambiguous word sequence. In the other condition, an identical syntactically ambiguous structure was used to describe only one situation. Sentences that could describe two situations had an ambiguous prepositional phrase attachment as in ‘‘I want to move the square with the triangle,’’ in which the move involved either a combined square-and-triangle piece or a triangle pushing a square to another position. Sentences describing only one situation involved only a cylinder pushing the square as in ‘‘I want to move the square with the cylinder.’’ Phonological analyses and phonetic analyses of duration and fundamental frequency were compared. Results indicate that speakers used prosodic phrasing to reflect situational syntactic ambiguity. Examples of relatively high and low variability in production will be discussed. [Work supported by NIH grant MH-51768, NZ/USA Cooperative Science Programme grant CSP95/01, Marsden Fund grant VUW604, and NIH research DC-00029.]
The basic units of rate normalization
Authors: Burnham Jessica L. , Newman Rochelle S.
Published: July 2002

We investigated the units of rate normalization, and found that they are not based on phonemes, but on segments with obvious acoustic boundaries, emphasizing the role of basic auditory processing in speech recognition. Individuals vary their speaking rate, and listeners use the duration of adjacent segments to adjust for these changes [J. Miller and A. Liberman, Percept. Psychophys. 25, 457–465 (1979)]. However, it has not been clear what these segments actually are. We examined whether two-phoneme sequences would produce two separate rate normalization effects (one for each phoneme), or only a single effect. We first used the series shkas–chkas, and examined effects of /k/ and /a/ duration on perception of the initial contrast. Altering the /k/ duration resulted in a rate normalization effect separate from that caused by varying the duration of the sequence as a whole. This suggests /k/ and /a/ are treated as separate units of speech. A /w/+vowel sequence showed a different result. For sequences such as ka, with obvious acoustic boundaries, each phoneme has a separate rate normalization effect. However, for sequences such as w, without such obvious cues, the sequence is treated as a single (larger) segment by the rate normalization process.
Time-frequency filters for target classification
Authors: Chevret P. , Gache N. , Zimpfer V.
Published: July 2002

This paper presents a new sonar target classification approach based on the use of time-frequency filters. Their design is carried out from the free field response of a reference target, and more precisely from the analysis of echo formation mechanisms in the time-frequency plane. The study of the relevance and the robustness of this approach in approximately real sonar conditions is conducted from experimental measurements in a tank. A data base is set up that contains a large set of target responses in the free field, near different interfaces and in waveguide situations. First, the efficiency of the method for the recognition of a nickel molybdenum spherical shell, corresponding to a class of man made targets whose size is much smaller than the sonar beam (finite size) is shown (100% of recognition). Second, a classification procedure between different targets of finite size is conducted: more than 85% of good classification is obtained (except for the marble solid target). Finally, in the presence of numerical noise, the method is found to be robust even for a low signal to noise ratio.
Learning to discriminate reduced-channel /bɑ/–/wɑ/ syllables in normal-hearing adults
Authors: Bahner Cammy L. , Carrell Thomas D. , Decker T. Newell
Published: July 2002

Acoustic information delivered to individuals with cochlear implants differs in many ways from the same information delivered via a normally functioning cochlea. One difference is that the number of frequencies that can be distinguished is sharply reduced in implanted listeners. This results in poor frequency selectivity where only sounds that fall into different frequency bands are distinguishable (all other things being equal). Shannon [Science 270, 303–304 (1995)] used an electrical filtering and rectification system to simulate this aspect of cochlear implant function in normal-hearing listeners. In the present study software filtering was combined with envelope-shaped-noise (ESN) processing to accomplish the same end. The immediate goal was to examine the efficacy of a simple technique in training listeners to distinguish between reduced-channel versions of syllables. The stimuli tested were synthetically produced /bɑ/ and /wɑ/ syllables, identical in every aspect except for their onset duration. These syllables were filtered into eight frequency bands and ESN processed. Following this they were once-again filtered at the same frequencies to create reduced-channel versions of the original syllables. The resulting stimuli were presented to 16 normal-hearing adult subjects in behavioral and electrophysiological tasks. Results demonstrated that the training rapidly improved listeners’ abilities to identify reduced-channel /bɑ/ and /wɑ/.
Surface waves over a convex impedance surface
Authors: Wang Qiang , Li Kai Ming
Published: July 2002

The existence of the surface wave in an upward refracting medium has been predicted by Raspet et al. [J. Acoust. Soc. Am. 89, 107–114 (1991)]. Making use of an acoustic analogy, one is able to study the surface waves above a convex cylinder and, hence, to simulate the propagation of sound over an impedance ground in an upward refracting medium. A suitable comblike surface may be used to facilitate the generation of surface waves above the convex ground. This paper describes laboratory experiments for the observation of surface waves over a convex impedance ground.
The influence of early reflections on the identification and lateralization of vowels
Authors: Watkins Anthony J.
Published: July 2002

Sound coming directly from a source is often accompanied by reflections arriving from different directions. However, the “precedence effect” occurs when listeners judge such a source’s direction: information in the direct, first-arriving sound tends to govern the direction heard for the overall sound. This paper asks whether the spectral envelope of the direct sound has a similar, dominant influence on the spectral envelope perceived for the whole sound. A continuum between two vowels was produced and then a “two-part” filter distorted each step. The beginning of this filter’s unit-sample response simulated a direct sound with no distortion of the spectral envelope. The second part simulated a reflection pattern that distorted the spectral envelope. The reflections’ frequency response was designed to give the spectral envelope of one of the continuum’s end-points to the other end-point. Listeners’ identifications showed that the reflections in two-part filters had a substantial influence because sounds tended to be identified as the positive vowel of the reflection pattern. This effect was not reduced when the interaural delays of the reflections and the direct sound were substantially different. Also, when the reflections were caused to precede the direct sound, the effects were much the same. By contrast, in measurements of lateralization the precedence effect was obtained. Here, the lateral position of the whole sound was largely governed by the interaural delay of the direct sound, and was hardly affected by the interaural delay of the reflections.
A high-resolution spectral estimation approach for evaluating the resonances of scattering returns from submerged targets
Authors: Lu I-Tai , Wu Fu-Po
Published: July 2002

The principal aim of this work is to estimate the complex resonant frequencies of scattering returns from the Mock-0 target. The experiments were conducted at the Naval Undersea Warfare Center. First, the singular value decomposition approach is employed for noise suppressing prefiltering where the initial estimate of the system order is obtained. Second, the eigen-matrix pencil method is employed to approximate the complex resonant frequencies. Finally, the system order and the complex resonances are determined by a systematic procedure in which the estimated results obtained from various system orders and aspect angles are compared. Echoes observed at the same aspect angle but excited by different incident pulses with overlapping frequency spectra can also be employed to obtain reliable estimations of resonant frequencies. The key feature of the proposed approach is robustness.
Acoustic X-wave reflection and transmission at a planar interface: Spectral analysis
Authors: Shaarawi Amr M. , Besieris Ioannis M. , Attiya Ahmed M. , El-Diwany Essam
Published: July 2002

The spectral structure of a three-dimensional X-wave pulse incident on a planar surface of discontinuity is examined. Introducing a novel superposition of azimuthally dependent pulsed plane waves, it is shown for oblique incidence that the reflected pulse has a localized wave structure. On the other hand, the transmitted field maintains its localization up to a certain distance from the interface, beyond which it starts disintegrating. An estimate of the localization range of the transmitted pulse is established; also, the parameters affecting the localization range are identified. The reflected and transmitted fields are deduced for X-waves incident from either a slower medium or a faster one. For the former case the evanescent fields in the second medium are calculated and their explicit time dependence is deduced for a normally incident X-wave. Furthermore, at near-critical incidence the transmitted pulse exhibits significant pulse compression and focusing.
Chirp response of an active-controlled thickness-drive tunable transducer
Authors: Alwi Hasan A. B. , Carey John R. , Smith Brian V.
Published: July 2002

The chirp response of a thickness-drive tunable transducer for wide range time-bandwidth and sweep rates chirp signals is demonstrated experimentally and computationally. The computational evaluation uses recursive digital-filter model based on the z-transform method. The model is limited to simple lossless structure with no front and backing layers. The model and experimental results show that there is no limit on the maximum sweep rate of the chirp signal but practically the limit is determined by the limitation of the circuit that generates the control voltage that simulates a variable electric load.
On the mechanoelectrical coupling in the cochlear outer hair cell
Authors: Spector Alexander A.
Published: July 2002

Outer hair cell electromotility, a manifestation of the interconnection between the mechanical and electrical processes occurring in outer hair cells, is believed to be an important contribution to the active cochlea. Two modes of mechanoelectrical coupling in the outer hair cell wall are studied: the potential shift caused by mechanical loading under the wall charge preservation conditions and the current (transferred charge) caused by mechanical loading under the voltage-clamp conditions. By using the previously reported elastic moduli of the wall and components of the active force, the potential shift under the charge preservation conditions is derived. This shift is expressed in terms of the wall strains and the active force derivatives with respect to the wall potential. The magnitudes of the potential shift corresponding to the conditions of cell inflation, axial stretch (compression), and the micropipet aspiration are estimated. In the last case, the distribution of the potential shift along the cell wall is also demonstrated. The potential shift can reach −20–−40 mV under the conditions of the micropipet aspiration or cell inflation. Such shift is much smaller under the condition of cell stretch (compression). The current and the charge transfer caused by the cell stretch under the voltage-clamp conditions is analyzed, and shows good agreement of predictions with experimental data.
Power law absorption in polymers and other systems
Authors: Wintle H. J.
Published: July 2002

The theoretical treatment of acoustic absorption which goes as a power of the frequency is quite subtle. In this paper, it is shown that some of the difficulties can be resolved by using a wide distribution of relaxation times which is cut off at a short time limit τ1>0, and a finite long time limit τ2<∞, without altering the general form of the acoustic response. This formalism is used to show that quadratic, linear, and fractional losses can be consistent with the Kramers–Kronig (KK) causal relations. The linear loss in polymers is associated with a weak velocity dispersion, so the group velocity and the phase velocity are quite close. The implications for space charge measurements in insulating polymers are discussed. Using the Helmholtz–Kirchhoff tube absorption as an example, it is also shown that the local approximation for the KK relations is unsatisfactory.
Experimental results for multichannel feedforward ANC with noninvasive system identification
Authors: Nowlin William C. , Guthart Gary S. , Toth Gregory K.
Published: July 2002

This paper presents experimental validation of a class of algorithms designed to enable active noise control (ANC) to function in environments when transfer functions change significantly over time. The experimental results presented are for broadband, local quieting in a diffuse field using a multichannel ANC system. The reverberant enclosure is an ordinary room, measuring approximately 1.4×2.4×2.4 m3 and containing a seated occupant, with six microphones defining the quiet zone near the occupant’s ears. The control system uses a single reference signal and two error channels to drive four secondary sources. Using an ideal reference sensor, reduction in sound pressure level is obtained at the quiet-zone microphones averaged over the frequency range 50 to 1000 Hz with an occupant seated in the room. Two main results are presented: first for an adaptive cancelling algorithm that uses static system models, and second for the same algorithm joined with a noninvasive real-time system identification algorithm. In the first case better than 23 dB of performance is obtained if the occupant remains still through calibration and testing. In the second case, approximately 18 dB is obtained at the error microphones regardless of the motion of the occupant.
Contributions of suppression and excitation to simultaneous masking: Effects of signal frequency and masker-signal frequency relation
Authors: Gifford René H. , Bacon Sid P.
Published: July 2002

This study investigated the contributions of suppression and excitation to simultaneous masking for a range of masker frequencies both below and above three different signal frequencies (750, 2000, and 4850 Hz). A two-stage experiment was employed. In stage I, the level of each off-frequency simultaneous masker necessary to mask a signal at 10 or 30 dB sensation level was determined. In stage II, three different forward-masking conditions were tested: (1) an on-frequency condition, in which the signals in stage I were used to mask probes of the same frequency; (2) an off-frequency condition, in which the off-frequency maskers (at the levels determined in stage I) were used to mask the probes; and (3) a combined condition, in which the on- and off-frequency maskers were combined to mask the probes. If the off-frequency maskers simultaneously masked the signal via spread of excitation in stage I, then the off-frequency and combined maskers should produce considerable forward masking in stage II. If, on the other hand, they masked via suppression, they should produce little or no forward masking. The contribution of suppression was found to increase with increasing signal frequency; it was absent at 750 Hz, but dominant at 4850 Hz. These results have implications for excitation pattern analyses and are consistent with stronger nonlinear processing at high rather than at low frequencies.
Scaling of turbulent wall pressure fluctuations downstream of a rearward facing step
Authors: Lauchle Gerald C. , Kargus Walter A.
Published: July 2002

The turbulent boundary layer that forms downstream of a surface discontinuity is locally inhomogeneous. Here, we consider the boundary layer that occurs downstream of a rearward facing step discontinuity on a flat plate that is exposed to a zero incidence, uniform subsonic flow. The wall pressure “point” spectra are measured by small, flush-mounted pressure transducers located at various locations downstream of the step. A new form of the nondimensional point wall pressure auto-frequency spectrum is proposed that includes the statistical variations of the reattachment location. This form is shown to collapse quite well all of the spectra measured slightly upstream, within, and downstream of the flow reattachment location.
Things that are and things to come for the Society’s publications: a myopic viewpoint
Authors: Pierce Allan D.
Published: July 2002

Several impending changes involving the Journal are discussed. These include proactive steps to facilitate publication of papers dealing with practical applications and of papers that may be helpful in the teaching of acoustics. Also discussed are virtual journals, the association of the Journal with Acoustic Research Letters Online (ARLO), possible changes in the handling of manuscripts, the desirability of encouraging good and concise writing, and the imposition of mandatory page charges for lengthy articles.