bluuebunny/crossref_metadata_2025 huggingface dataset:
Playback experiments with long-finned pilot whales using a new broadband transmitter
Authors: Jones Dennis F. , Rendell Luke E.
Published: July 2002

Recently, a portable broadband acoustic transmission system (BATS) was developed as a joint venture between the Defence Research Establishment Atlantic and Sensor Technology Limited in Collingwood, Ontario. This transmitter is battery operated, easily deployed from small research vessels, and can produce source levels of 165 dB//1 μPa-m throughout its 1–14 kHz operating frequency band. The BATS was used by researchers from the Whitehead Laboratory at Dalhousie University to investigate vocal mimicry in long-finned pilot whales (Globicephala melas) off the coast of Cape Breton Island, Nova Scotia during the summer of 1999. A series of frequency-modulated tones in the 2–10 kHz band and using 33 cycles was played back to the pilot whales from the BATS and the acoustic responses were recorded using a hydrophone and tape recorder. Evidence that the whales heard these stimuli was extracted from the recordings and estimates of received levels were made. Although there were no instances of clear mimicry of the stimuli, there were a few tantalizing whale vocalizations that have highlighted the need for further experimentation. [Work supported in part by NSERC, Canada.]
Inversion for geometric and geoacoustic parameters of Haro Strait data using a posteriori density functions
Authors: Viechnicki John , Chapman Ross
Published: July 2002

Inversions for geometric and geoacoustic parameters of a multitone, multishot experiment are examined using a posteriori probability distributions based on simulated annealing importance sampling. Data were collected as part of the matched-field tomography component of the Haro Strait PRIMER Experiment of June/July 1996 which can be categorized as low frequency, shallow water, and bathymetrically complex. The inherently unquantifiable sources of mismatch between data and model in environmentally complex systems favor a statistical approach over more conventional global optimization techniques. Large uniqueness and parameterization error complicate an accurate interpretation of the data covariance matrix necessary for appropriate choice of Gibbs sampling temperature. Trends in density functions are therefore examined as the relative sampling temperature is lowered. The mean and half-width value of the density distribution for each parameter are evaluated as a function of sampling temperature. [Work supported by ONR.]
Inversion of sediment parameters in a shallow-water range-dependent environment
Authors: Potty Gopu R. , Miller James H.
Published: July 2002

The propagation of acoustic energy in a range dependent environment will be analyzed. The broadband acoustic signals from explosive sources collected during the Shelf Break PRIMER Experiment will be used for this study. Time–frequency behavior of these signals will be analyzed using wavelets. Upslope propagation along varying bathymetry (from 800 m at source location to 90 m at the receiver) and sound speed is considered. A simple model for the sediment compressional speeds will be extracted using a hybrid inversion scheme. This hybrid scheme uses a genetic algorithm and Levenberg–Marquardt nonlinear least-squares method. Inversion is based on group speed dispersion. Theoretical group speeds will be calculated based on range-dependent propagation. [Work supported by ONR.]
Determining a geoacoustic model from shallow-water transmission loss data using parameter linkage and a hybrid inversion algorithm
Authors: Hall Marshall V.
Published: July 2002

In order to characterize the propagation conditions along a shallow-water sound range at low frequencies, measurements have been made of both cw transmission loss versus distance, and travel times of airgun-generated head waves. The head wave data yield the sound speed and time intercept of a reflecting interface, and these results are used as known parameters when the cw data are inverted to obtain a complete geoacoustic model. The inversion algorithm was a hybrid of the simplex and simulated annealing methods, similar to versions developed recently at the University of Victoria, Canada. The geoacoustic model was assumed to consist of two uniform solid layers overlying a solid uniform basement. The sound speed of the upper layer was estimated from the measured seafloor grain size, in accordance with empirical data. To further reduce the number of parameters, regression equations were devised to relate the less critical parameters (density, shear speed, and shear absorption) to those that are usually found to be more important (sound speed, sound absorption, and layer thickness), although the basement shear speed was also found to be an important parameter. With only six unknown parameters, the inversion algorithm generally found a satisfactory geoacoustic model after only several hundred runs.
A genetic algorithm for sediment sound-speed profile estimation from source and receiver position and travel time data
Authors: McCurley Brett , Chotiros Nicholas P. , Piper James , Smith Eric
Published: July 2002

Data were taken from a source projecting sound (10 to 100 kHz) at low grazing angles to a buried array (at a 30-deg decline) of nine receivers. These data were collected in October 1999 as part of the Sediment Acoustics Experiment (SAX99) off the coast of Fort Walton Beach, Florida. From the source and receiver positions and accurate measurements of travel time, the sound-speed profile can be estimated from the water–sediment boundary to the deepest receiver. The relationship between sound speed and depth can be determined. Also, refraction layers within the sediment can be ascertained. This estimation can be accomplished with the use of a genetic algorithm that searches a given sound-speed range to estimate the speed profile at specific frequencies. The algorithm equates the known travel time to the time associated with the refracted sound to each receiver position (distance from source). [Work supported by ONR, Ocean Acoustics.]
Clinical applications of acoustical microscopy
Authors: Jones Joie P.
Published: July 2002

Very high frequency ultrasonic imaging offers an important tool for biomedical research as well as for clinical practice. Using ultrasound systems operating between 20 and 200 MHz, morphological and functional images of the skin may be obtained. For example, ultrasound may be used to assess wound healing, determine the extent of skin tumors, measure skin thickness, and visualize skin vascularization. At higher frequencies (600 to 1000 MHz), ultrasonic imaging can be used for histological studies with far greater sensitivity than optical microscopy and with a spatial resolution equivalent to optical methods. For example, ultrasound may be used to evaluate biopsy specimens more quickly and more accurately than optical microscopy. Here we report our experiences with very high frequency ultrasound as a clinical tool and, using this technology, the development of new standards by which tissue changes and disease processes may be defined.
Microbubbles and medical ultrasound: Optimization of harmonic imaging
Authors: Wyczalkowski Matthew , Szeri Andrew J.
Published: July 2002

Due to their nonlinear nature, bubbles driven at a particular frequency will radiate a considerable portion of their total acoustic emission at a frequency twice that of the driving—at the second harmonic. Tissues in the body, however, radiate predominantly at the driving frequency only. In ultrasound applications where bubbles serve as contrast agents, this effect leads to reduced noise at the second harmonic and forms the basis of harmonic imaging. This paper explores techniques by which the amount of energy radiated by a bubble at a frequency of twice the driving may be increased. A modulating signal of a frequency distinct from the fundamental is added to the forcing. The amplitude and phase of the modulating signal are chosen so as to be optimal; that is, so as to maximize a particular measure of the acoustic response. Results are presented for several different schemes of multimode forcing. The total acoustic emission, as well as emission at the first and second harmonics, is obtained for bubbles of a spectrum of sizes and a range of amplitudes of the driving. These results are compared with the response of bubbles at the single-frequency forcing.
New and old approaches for nonlinear-contrast agents imaging
Authors: Sutin Alexander M.
Published: July 2002

Microbubble, nonlinear-contrast agents are used in nonlinear ultrasound imaging to increase the contrast between these agents and the surrounding tissue. Similar approaches were developed in Russia in the 1980s for bubble measurements at sea. Two methods can enhance nonlinear imaging. (1) Sum-frequency nonlinear imaging has several advantages over second harmonic imaging due to the absence of nonlinear distortion in electronic circuits and emitters. This method allows one to use significantly less ultrasound amplitude than in the method of second harmonic imaging. This method was used for bubble detection in sea sediments. (2) The nonlinear difference frequency Doppler effect is based on moving bubbles that are insonified by two acoustic beams of different frequencies directed from different directions. Difference-frequency scattering provides significant enhancement of the Doppler frequency shift. This method was tested in laboratory conditions. Nonlinear scattering by microbubbles could also lead to remote, direct blood-pressure measurements. This method could be based on measurements of microbubble resonance frequencies by using nonlinear scattering. The resonance frequency depends on the ambient pressure; nonlinear scattering provides high-resolution measurements of the resonance frequencies and avoids the influence of scattered signals reflected by different inhomogeneities in the human body. [Work was supported by Stevens.]
Bessel beams of finite amplitude in absorbing media
Authors: Cunningham Kevin B. , Hamilton Mark F.
Published: July 2002

The profile of a Bessel beam is J0(ρ), where J0 is the zeroth-order Bessel function and ρ is a dimensionless distance from the axis. The beam propagates without diffraction, a property that has stimulated interest in connection with medical ultrasound imaging. Previous analyses of second-harmonic generation in Bessel beams are limited to lossless media. Du, Zhang, and Zhu [Proc. 14th Intl. Symp. Nonlin. Acoust., edited by R. J. Wei (Nanjing U.P., Nanjing, 1996), pp. 189–194] showed that the beam profile of the second harmonic in the near field is given approximately by J20(ρ). Ding and Lu [Appl. Phys. Lett. 68, 608 (1996)] obtained J0(2ρ) for the far field. We provide a more general analysis of second-harmonic generation, first by investigating solutions for lossless propagation in greater detail, and second by including absorption. It is shown that the far-field beam profile is J0(2ρ) only for very small values of a characteristic absorption parameter. As the absorption parameter increases, the beam profile evolves toward a distribution given approximately (i.e., away from minima) by J20(ρ). Numerical results are presented for higher harmonics and for waveform distortion in a Bessel beam that forms a shock. [Work supported by ONR.]
Developing a simple heuristic viscoelastic theory of piezoelectricity
Authors: Smith R. Lowell
Published: July 2002

In its simplest form, the linear theory of piezoelectricity takes no account of losses or dissipation phenomena in electroactive materials. This deficiency is often addressed by allowing the dielectric, mechanical, and piezoelectric coefficients to be represented as complex numbers. This paper discusses a related exercise in which the electroactive material is considered to be a three-parameter viscoelastic solid. The piezoelectric equations are redeveloped via the incorporation of a generalized version of Hooke’s law representing a single relaxation process. Through examination of the responses of the system in creep, stress relaxation, and dynamic loading scenarios, the time and frequency dependences of the associated relaxation and dynamic compliances are inferred. The formalism is applied to a simple longitudinal vibrator geometry, and it is demonstrated that primitive viscoelastic behavior can be advantageously described using standard equivalent circuit analogies. The method can readily be generalized to accommodate more complete viscoelastic models.
Application of Lamb waves to characterize adhesive bond properties
Authors: Seifried Robert , Jacobs Laurence , Qu Jianmin
Published: July 2002

This research develops an analytical model that quantifies the effect of an adhesive bond’s properties, on the propagation of guided ultrasonic waves in a three-layered, adhesively bonded component. A separate experimental study has developed the relationship between a bonded specimen’s dispersion spectrum (the modes in its frequency-wave number relationship), and the condition of the adhesive bond; these experiments show that bond degradation causes some of the specimen’s higher modes to damp-out and vanish. The goal of the current research is to develop a theoretical understanding of this experimentally observed behavior; a fundamental understanding of the mechanics of this phenomenon is needed to develop a quantitative nondestructive evaluation procedure, capable of measuring the stiffness of a bonded component. A continuum mechanics based model for the steady-state propagation of guided waves in a three-layer component is developed. This model enables a parameter study—by varying the adhesive bond’s material properties—to quantify the effect of the adhesive’s properties on the (overall) bonded component’s dispersion curves, thus characterizing the effect of aging. In addition, the transient behavior of the bonded component is established with a finite element model.
Recent experiences with electronic acoustical enhancement in concert halls, opera houses, and outdoor venues
Authors: Griesinger David , Barbar Steve
Published: July 2002

This paper gives a brief summary of acoustical theory based on human perception. It then uses this theory to discuss the design criteria and performance data of electronic acoustic-enhancement systems installed in a number of venues. The installations include the Deutches Staatsoper in Berlin, the Hummingbird Centre in Toronto, the Circle Theatre in Indianapolis, the Adelaide Festival Centre Theater in Adelaide, Australia, and Morbisch FestSpiele in Austria. Solutions to the problems of maintaining optimum clarity while providing optimum envelopment are given.
Appreciation of the SIAP system by the audience, performers, and theater management
Authors: Kok Ben , Prinssen Wim
Published: July 2002

Over the past decade, numerous acoustic enhancement systems based on SIAP technology have been installed. Although the design concept and implementation have been proven by the objective results, this itself does not guarantee artistic acceptance by audience and performers. Most SIAP installations are being used without much comment and often the performers and/or the audience are not aware of the electronic modifications to the natural acoustics of the auditorium. This makes it difficult to measure the artistic acceptance. In some situations, however, the installation of the SIAP system was a turning point in the appreciation, thus exploitation, of the theater. After a brief introduction on what sets the SIAP system apart from other enhancement systems, this paper will give some examples of projects where the installation of an SIAP system had a positive influence on the audience attendance and appreciation by the performers.
Auditory sensitivity in woodpeckers
Authors: Lohr Bernard , Brittan-Powell Elizabeth F. , Dooling Robert J. , Pater Larry
Published: July 2002

While there are numerous behavioral and physiological studies of hearing in small birds, there are no studies of hearing in woodpeckers. Woodpeckers are particularly interesting because they exhibit a variety of cranial adaptations that may influence auditory sensitivity. The present study examined auditory sensitivity in small woodpeckers using the cochlear microphonic (measured subdermally and in the cochlea) as a means of estimating hearing thresholds. Subjects were presented with both rectangular-pulse clicks and tone-burst stimuli. Clicks were 0.1 ms in duration and were presented in ascending order from 30–100 dB SPL. Tone bursts were 5 ms in duration with a 1-ms rise/fall, and were presented in ascending order from 30–100 dB SPL at frequencies ranging from 500–8000 Hz. Thresholds were computed from latency-intensity and amplitude-intensity functions at all frequencies. Results suggest that hearing abilities of woodpeckers are similar to those of other small birds. [Work supported by SERDP.]
Discrimination of Shepard tones by a song bird
Authors: Cynx Jeffrey
Published: July 2002

We know relatively little about how songbirds perceive harmonic structures. This research investigated whether songbirds, like humans, can perceive pitch classes when pitch height is experimentally controlled. Humans, when presented with tone intervals controlled for pitch height (Shepard tones), perceive the intervals as either rising or falling according to closeness on a pitch class or octave circle. A special interval with these stimuli is the half octave (or tritone), as it is equidistant in the rising and falling directions on the octave circle. Songbirds, trained to discriminate rising versus falling intervals, showed an ability to perceive the Shepard tones also as rising or falling.
Hearing and vocalizations in the orange-fronted conure (Aratinga canicularis), a small parrot
Authors: Wright Timothy F. , Dooling Robert J. , Cortopassi Kathryn A , Bradbury Jack
Published: July 2002

The orange-fronted conure (Aratinga canicularis) is a small Neotropical parrot that is the subject of an ongoing study of vocal communication and social organization. Three captive-bred orange-fronted conures were trained to detect pure tones using operant conditioning with a food reward and tested using the method of constant stimuli. These birds were tested at seven frequencies ranging from 0.5 to 8 kHz. The greatest sensitivity was found between 1 and 4 kHz and lower sensitivity outside this region. The shape of the audiogram for this species was similar to those previously found for three other species of small parrots, but the absolute sensitivity for orange-fronted conures was generally lower than these other parrot species at most frequencies. The range of greatest sensitivity in the orange-fronted conures corresponded fairly well with the spectral characteristics of their contact calls. In a sample of 288 contact calls recorded from eight wild birds in Costa Rica, the mean peak frequency of the calls was 3371 Hz with a SD of 341 Hz, and the bulk of spectral energy fell between 2295 and 5231 Hz. [Work supported by NIH Grant No. R01 DC00198 (RJD), NRSA Fellowship Nos. DC00046 and MH12111 (TFW), and a NSF grant (JB and KAP).]
Ultrasound mediated drug delivery—A new era using ultrasound contrast agents?
Authors: Unger Evan C.
Published: July 2002

Ultrasound has been used therapeutically for decades. High energy ultrasound is used clinically in hyperthermia. Transdermal drug delivery is accomplished with ultrasound, perhaps more effectively at low frequencies because of more efficient cavitation. High intensity focused ultrasound (HIFU) is used to coagulate tissue for treatment of cancer and hemostasis. Recently, contrast agents have been developed for diagnostic ultrasound. These agents can also be used as exogenous cavitation nuclei for therapy. Compared to some of the other therapeutic ultrasound techniques, exogenous cavitation nuclei may enable use of lower power levels. Applications of ultrasound contrast agents as cavitation nuclei include sonothrombolysis and drug and gene delivery. Cavitation of contrast agents can be used to increase capillary permeability to deliver drugs. Co-administration of ultrasound contrast agents with transdermal ultrasound accomplishes sonothrombolysis. Acoustically active carriers (contrast agents) have been developed to carry drugs and genes; systemic administration produces local drug delivery within the field of insonation. Contrast agents may open a new era of therapeutic applications of ultrasound for drug delivery and sonothrombolysis.
Focused ultrasound opens the blood–brain barrier in vivo
Authors: Mourad Pierre D. , Crum Lawrence A. , Mesiwala Ali , Winn H. R. , Silbergeld Daniel L.
Published: July 2002

The blood–brain barrier (BBB) consists of specialized endothelial cells that line the capillaries within the brain whose overlapping regions are held firm by ‘‘tight junctions.’’ In the central nervous system (CNS) the BBB plays a protective role, restricting the movement of molecules into the brain. It is also the major impediment to the flux of therapeutic drugs into the CNS. High-intensity focused ultrasound (HIFU) has been shown to induce the displacement of ordinarily impermeable vital dyes from the blood stream into the brain without damage to the CNS in the proximity of the flux. However, there has been no elucidation of the biological response to ultrasound that allows this flux. We show using a rat model that, by opening the tight junctions or by causing the endothelial cells to retract, HIFU can selectively disrupt the BBB in a reversible, controlled manner without injury to the surrounding CNS. Moreover, this effect reverses within 96 h. We believe that this work will lay the foundation for the development of therapies designed to optimize and take advantage of this novel biological response to ultrasound.
A real-time binaural loudness meter
Authors: Tuomi Olli , Zacharov Nick
Published: July 2002

The alignment of sound intensity is of great importance, particularly in the field of psychometrics. When sounds have different spectral content, loudness alignment becomes a more suitable tool. However, traditional models assume the source either to reside in a free field at 0 azimuth or in a diffuse field. To assess or align sound-source loudness at different locations or with different radiation characteristics is more problematic. This paper presents the development of a real-time loudness meter based around the Moore loudness model. The tool has been developed in c and matlab and supports both diffuse and free-field microphone input on a minimal hardware PC platform, with a generic sound card. Furthermore, binaural input to the model has been developed for a head and torso simulator (HATS). Use of a HATS allows for compensation of directional loudness properties caused by the head and pinna. It is thus possible to assess or align reproduction systems of different directivities or with different number of sources in either a monaural or binaural sense. Automatic calibration allows for easy alignment for calibrated use with either microphone or HATS. The system is presented and verification results given under different test conditions.
Inclusion of wave-front steepening in a frequency-domain model of trombone sound production
Authors: Thompson Michael W. , Strong William J.
Published: July 2002

This research investigates the modeling of harmonic generation occurring in trombone sound production at loud dynamic levels. The profile of a tenor trombone was approximated as a set of contiguous cylindrical tubes. A linear model of the trombone was obtained by requiring continuity of pressure and flow between adjacent tubes. The mouthpiece and radiated pressure spectra were measured in an anechoic chamber for several pitches played in first position at several dynamic levels. The measured mouthpiece spectra were processed by the model, taking into account harmonic generation due to wave-front steepening. Results comparing the calculated radiated spectra with the measured radiated spectra will be reported, along with an overview of the algorithm.
Determination of the frequency vibrato extent based on the linear predictive coding parameters
Authors: Diaz Jose , Arroyo Antonio , Rothman Howard
Published: July 2002

Many time-domain signals can be modeled as a sum of sinusoids whose main parameters are amplitude and frequency. The frequency can be obtained from the linear predictive coding (LPC) parameters by the pole location in the Z-domain. Although intuition dictates that the amplitude could also be obtained from the LPC parameters, there appears to be no information available that would allow its computation. The purpose of this research is to investigate the relationship between the LPC parameters and the amplitude of a wave in the time domain. In order to accomplish this, the power spectrum obtained using the LPC method was plotted against the FFT spectrum of vibrato samples. They were then compared, and several parameters of the LPC spectrum were changed until both spectra matched. From these matched spectra, the wave amplitude was obtained. This new method was then used in an application to determine the time-varying amplitude of the vibrato wave. This served two purposes: first, to verify the accuracy of the method, and second, to show the usefulness of the time-domain parameters. The results show that there is a direct relationship between the LPC parameters and the amplitude of a wave in the time domain.
Comparison of percentile and equivalent sound level criteria for construction projects
Authors: Tocci Gregory C.
Published: July 2002

Community ordinances and construction specifications widely use equivalent sound levels, and more often maximum sound pressure levels, to establish limits on environmental noise. In the case of construction, limits on noise expressed as maximum sound levels or equivalent sound levels can be either unreasonably permissive or unreasonably restrictive. It will be argued and shown that expressing construction noise limits as percentile sound levels offers a more realistic assessment of noise impact and can be more useful in understanding construction noise impacts. This presentation will discuss the advantages and disadvantages of limits expressed as equivalent sound levels, maximum sound levels, and percentile sound levels. Methods of analysis and results using each type of descriptor will be discussed. These methods will be compared using actual probability density functions and equivalent sound levels measured for construction operations. The presentation will close with the author’s suggestions for managing construction noise control projects on the basis of his firm’s 20 years of experience conducting construction noise and vibration analyses on a wide variety of construction projects including highway, transit, and building projects.
Protecting pedestrians from open construction activities
Authors: Raichel Daniel R. , Dallal Michael
Published: July 2002

During the course of a project that was conducted for New York City’s Department of Design and Construction, it was observed that many urban construction activities occur in open areas, involving street repaving, overhaul of utility lines, sidewalk repairs, etc. Equipment such as backhoes, jackhammers, air compressors, and pavement saws generate extremely loud noises, often exceeding 100 dB(A) at 5 or 6 m. Passersby, exposed to the cacophony without the benefit of any intervening barriers, are as close as 0.4 m to the noise-generating equipment. An additional peril to passing pedestrians exists in debris flying from the breakup of concrete, asphalt, or metal. It was also noted that many pedestrians, even those suffering the threshold of pain from the noise, will not go out of their way to a quieter section of the street. Hence, a need exists to establish and enforce regulations to protect pedestrians from such open construction activities. Noise barriers can do double duty in preventing the scattering of debris and mitigating noise. Portability and reusability constitute the requirements for these barriers. But, contractors need to be educated on the proper deployment of these barriers and on the necessity for them.
A thermoacoustic traveling wave linear amplifier
Authors: Hiller Robert A.
Published: July 2002

This paper describes an experiment to show linear amplification of traveling sound waves in a duct using a thermoacoustic regenerator. As noted by Ceperley [J. Acoust. Soc. Am. 66, 1508–1513 (1979)] a Stirling engine-type regenerator should act as an acoustic gain medium for traveling waves in a duct. This principle is used in thermoacoustic traveling wave engines to transfer power from heat reservoirs to acoustic energy. However, it is difficult to produce finite gain for pure traveling wave impedance, since viscous losses in the channels of the regenerator overcome the gain, and previous workers have only been able to show reduced loss in such a system. Optimizing the regenerator design with numerical modeling and using a greater temperature difference suggest that a traveling wave thermal amplifier can produce 2 dB of real gain over two octaves for traveling waves in air. Such a device would amplify a broadband acoustic signal without electrical transducers. Design of the amplifier and experimental results will be shown.
Beyond presbyacusis: Non-hearing loss-related temporal processing deficits in the elderly
Authors: Divenyi Pierre L.
Published: July 2002

A group of 56 elderly individuals were tested in a battery of tests including pure tone audiometry, various word- and sentence-level speech understanding tasks, and measurement of spectral, temporal, and spatial auditory abilities. Presbyacusic hearing loss, when present, was symmetrical in the two ears and at most mild to moderate, with no significant deficit below 1.5 kHz. Frequency resolution was estimated by calculating auditory filter width from notched-noise masking at 1 kHz; temporal resolution was estimated from gap discrimination and from auditory segregation of temporal patterns of harmonic complexes with components below 1.2 kHz (in the low envelope frequency range); spatial resolution in the horizontal plane was estimated from interaural time difference (ITD) thresholds for 500-Hz clicks. The largest differences between results of the elderly and those of normal-hearing young subjects were seen for speech understanding in spatially distributed babble, word recognition in reverberant rooms, ITD thresholds, and segregation of temporal patterns. The results portray the decline of temporal processing as an important component of auditory and speech understanding dysfunctions in aging and strongly suggest that a non-negligible part of these dysfunctions may be of central origin. [Supported by the National Institute on Aging and the V. A. Medical Research.]
Optimal design of Stockbridge dynamic vibration absorber viscoelastically modified by applying the finite element method
Authors: Floody Sergio , Espindola Jose
Published: July 2002

The present paper deals with an extension in the study of vibration absorbers applied to complex mechanical systems that are independent of geometry, mass, stiffness, and damping distribution by introducing the concept of equivalent generalized quantities. The basic idea is to transform the mechanical impedance, that the absorber transfers in the primary system’s point of connection, in generalized equivalent quantities of mass and damping that depends on the frequency. This methodology was applied in order to design a viscoelastically modified Stockbridge absorber by applying the finite element method extending the proposed theory of generalized equivalent quantities for several degrees of freedom that can be presented due to the characteristics of this absorber. Later, the genetic algorithm was used to minimize the frequency response of the joint system in order to obtain the optimal dimensions of this mechanical device.
State-switched absorber for control of beams
Authors: Cunefare Kenneth A.
Published: July 2002

A system that has the capability to make instantaneous changes in its mass, stiffness, or damping may be termed a state-switchable dynamical system. Such a system will display different dynamical responses dependent upon its current state. State-switchable stiffness may be practically obtained through the control of the termination impedance of piezoelectric stiffness elements. If such a switchable stiffness element is incorporated as part of the spring element of a vibration absorber, the change in stiffness causes a change in the resonance frequencies of the system, thereby instantaneously retuning the state-switched absorber to a new frequency. In between state switches, the operation of such a device is passive, being fundamentally a passive vibration absorber. This paper considers the application of such a device for the purpose of vibration control on beams.
Locus equation parameters in non-native speech
Authors: Oh Eunjin
Published: July 2002

The principled relation between the magnitude of CV coarticulation and the language-specific system of phonological contrasts was investigated by comparing slope values of the locus equation [Lindblom, J. Acoust. Soc. Am. 35, 1773–1781 (1963)] for three stop places of articulation in English and Russian. The slopes of the locus equation were hypothesized to be shallower in Russian, indicating less vocalic influences on adjacent stop consonants, than in English, due to the requirement maintaining the phonological distinctions between plain and palatalized stops imposed only on Russian [Cohn, UCLA WPP 69, 51–59 (1987)]. More importantly, this study compares the slope, y-intercept, and R-squared values of native speakers with those of English learners of Russian. Preliminary analyses on bilabial stops indicated the following. (i) The locus lines of Russian were characterized by substantially shallower slopes and larger y-intercepts than those of English. (ii) The locus lines of relatively experienced English speakers of Russian showed shallower slopes and larger y-intercepts than those of native English speakers. An advantage of investigating the locus equation parameters as indices of acquisition effects of CV coarticulation is that the locus equation parameters characterize the acquisition of coarticulatory regularities of a whole distribution of CV tokens, not just the acquisition of a single CV token.
Intrinsic versus interaction effects on F0
Authors: Kim Mi-Ryoung
Published: July 2002

This study investigates the nature and magnitude of the effect of segments, initial and final consonants, vowel quality, and vowel length on F0 contour in English and Korean. The two languages were compared with a special reference of the effect of initial consonants on F0. F0 was measured at three temporal locations of each syllable rime onset, midpoint, and offset. For Korean, of the four segment types, initial consonants had the greatest effect on F0 contour in both spectral and temporal magnitude, indicating that consonant types interacted with tone. The English data showed that the segmental influence reflected intrinsic effects on F0. In particular, the effects of initial consonants on F0 contours in English were significantly smaller in spectral and temporal extent than those of Korean. This study concluded that there are cross-linguistic differences between English and Korean concerning the effect of initial consonants on F0 contour (which I call ‘‘intrinsic’’ versus ‘‘interaction’’). The consonant–tone interactions in Korean are viewed as consistent with tonogenesis: voiceless (aspirated and tense) consonants correlate lead H and phonologically voiced (lax, sonorants, and zero) consonants lead LH. This is the first study that accounts for the Korean interaction phenomena by a theory of tonogenesis.
Recoverability constraints on gestural overlap in Georgian stop sequences
Authors: Chitoran Ioana , Byrd Dani , Goldstein Louis
Published: July 2002

Recent investigations of the temporal organization of articulatory gestures have found that consonants in a cluster exhibit less temporal overlap when in word-onset position than when the cluster occurs word-finally or spanning a word boundary. A possible reason for this is that substantial overlap of obstruent gestures in utterance-initial position may threaten their perceptual recoverability. Recoverability considerations may also account for results showing that a front-to-back order of place of articulation in stop–stop sequences (labial–alveolar, alveolar–velar, labial–velar) allows more overlap than the opposite order. Presumably, the recoverability of C1 is hindered if the release of C1 has no acoustic manifestation due to the presence of a more anterior C2 being coproduced in time, hiding the C1 release. Data demonstrating both these constraints on gestural patterning have previously been drawn only from English, limiting the type and position of consonant sequences. The Georgian language offers a rich inventory of consonant sequences including stop–stop sequences in initial, medial, and cross-word-boundary positions. This work is an articulator movement tracking study of two Georgian speakers producing such sequences. The results provide evidence that the sequence’s word position and the component consonants’ constriction locations both constrain the patterns of gestural overlap produced. [Work supported by NIH.]
Measurements of three-dimensional sound fields over different bottom types
Authors: Glegg Stewart , Cichock Joe
Published: July 2002

This paper will describe measurements of three-dimensional underwater sound propagation over a sloping bottom. For this study a laboratory scale model was used with a typical slope of 2 deg. In the first series of measurements the sediment was modeled using concrete, providing a rigid lower boundary. In the second series, the concrete was coated with an epoxy layer, giving a softer lower boundary. The sound fields in these two cases showed significant differences that will be illustrated. Earlier work has shown that the sound field over the rigid bottom included interference effects caused by bathymetric refraction. The results for the softer lower boundary did not show these features. The measurements will also be compared with N×2D PE calculations. [Work supported by ONR.]
Ray theory and waveforms at caustics
Authors: Tindle Chris T.
Published: July 2002

Waveforms for deep-water pulse propagation to a vertical array are calculated using a ‘‘measurement front’’ which is a continuous curve of arrival time as a function of depth. Each arriving pulse has a phase and amplitude determined by interpolation of the measurement front. The expressions for the phase and amplitude are derived directly from the wave equation using WKB expressions for the vertical dependence of the wave field. The measurement front contains caustics and the front is continued into the shadow using complex rays. The acoustic field on both sides of a caustic is calculated in terms of Airy functions. Detailed agreement with reference solutions is obtained.
Managing high-frequency losses in large venue sound-reinforcement systems
Authors: Siegel Stephen J.
Published: July 2002

The myriad of challenges associated with sound-reinforcement systems for arenas, stadiums, and outdoor festivals presents significant obstacles to the audio professional. One of the most significant factors, which can affect both speech intelligibility and tonal accuracy of sound reproduction, is loss of projection due to air absorption. On the surface it might seem that this is a very high-frequency phenomenon which would only be a concern for certain types of musical program. Closer examination reveals that it is, in fact, a significant factor at frequencies in the vocal range. The types of losses encountered in the arena, stadium, and festival configurations are examined, and their impact on both speech and music program is discussed. Methods to implement large-scale sound systems to mimimize these effects are presented, with several applications shown as examples.
Loudspeaker directivity as a function of frequency, and the importance thereof to sound system performance in large and reverberant spaces
Authors: Long James
Published: July 2002

Control of a loudspeaker’s directivity, or coverage pattern, at high frequencies can be readily achieved with devices of modest dimensions. Extending directivity control into the vocal midrange and below requires devices of significantly larger size and possibly greater complexity. However, directivity control at lower frequencies can significantly increase musical clarity and vocal intelligibility in large and typically reverberant spaces such as stadiums and arenas. The basic physics behind achieving extended frequency directivity control, including the use of signal processing, will be outlined. Typical existing, practical examples will be presented. A two-channel computer auralization comparing transducers in a reverberant space with and without extended frequency directivity control will be demonstrated.
Acoustics and sound-system design for the National Ice Centre, Nottingham, UK
Authors: Mapp Peter
Published: July 2002

The National Ice Centre, Nottingham is a unique indoor arena within the UK, as it will house two full-size ice pads both capable of hosting national and international ice-skating competitions. One of the ice pads will be permanently available for both local community (public) and professional ice-skating activities. The other pad, located in the main arena, can be covered over and the arena used to seat audiences of up to 10000 spectators for pop concerts, major artist performances, sports events (e.g., tennis or boxing), and large conferences/meetings/exhibitions/conventions. The main arena will also host national and international ice dance and skating competitions. With such a wide range of activities, considerable attention has been paid to both the acoustics of the place and the installed sound systems. The paper describes both the acoustic treatment of the arena and the design philosophy and testing of the complex sound systems. The sound-system design is unusual for such a venue in that two separate systems are installed to cater to both the performance sound and voice alarm (fire alarm) needs without compromising the strict requirements relating to public safety in a building of this nature and size.
Pitch perception versus target ranging and identification in echolocating bats
Authors: Shamma Shihab
Published: July 2002

When echolocating, the brown bat emits a train of FM pulses while listening to the echoes from the target. It then estimates the target range and identity based on the time intervals and interactions between the pulses and their echoes. These remarkable abilities are often thought to arise from unique neural computations and networks, since most other mammals do not echolocate. Furthermore, related physiological data are most commonly interpreted as indicative of temporal algorithms involving delay-tuned cells, auto-correlators, and other temporally accurate structures. In this talk, we shall argue that target ranging and target identification are in fact computationally identical to pitch estimation in other mammals; specifically, they are analogous to the perception of repetition pitch and of periodicity (or musical) pitch, respectively. We shall also discuss how these estimates can be derived from so-called spectrally based (rather than temporally based) algorithms, invoking harmonic series templates and instantaneous coincidences among cochlear outputs that do not require arrays of delay-tuned cells. These results offer alternative interpretations for the physiological evidence from bats and suggest close parallels between them and other nonecholocating mammals.
Sonoluminescence as an indicator of cell-membrane disruption by acoustic cavitation
Authors: Cochran Stephen , Prausnitz Mark
Published: July 2002

Acoustic cavitation has been shown to reversibly disrupt cell membranes and thereby transport molecules into viable cells. The hypothesis was that the light emitted during inertial cavitation, i.e., sonoluminescence, correlates with these acoustic bioeffects. In this study, sonoluminescence was measured using a photomultiplier tube mounted at the base of an opaque cavitation chamber. The bioeffects measured on DU 145 prostate cancer cells placed in the cavitation field included the number of molecules delivered into each cell and overall cell viability. A 24-kHz cylindrical piezoelectric transducer was used in these experiments to generate cavitation over a range of pressure levels, pulse lengths, and total exposure times. The results show that cells were reversibly disrupted, yielding extensive uptake of calcein by some cells, little uptake by other cells, and loss of viability for a third population of cells. Correlation with sonoluminescence indicated that light emission correlated with these bioeffects.
3D full wave ultrasonic field and temperature simulations in biological tissue containing a blood vessel
Authors: Curra Francesco P. , Mourad Pierre D. , Crum Lawrence A. , Khokhlova Vera A.
Published: July 2002

In order to simulate ultrasound propagation and subsequent thermal effects in biological media in which blood vessels and other structures may be present, a three-dimensional model has been developed that eliminates the need for symmetry constraints. The model is based on the coupled solution of the full wave nonlinear equation of sound in a lossy medium and the bioheat equation obtained by a pseudospectral finite-difference method in the time domain. It includes nonlinear sound propagation, an arbitrary frequency power law for attenuation, and is capable of treating material inhomogeneities. Unlike other models based on parabolic approximations, it is not restricted to near-axis solutions and can account for reflections and backscattered fields. The program was used to simulate the application of high-intensity focused ultrasound (HIFU) in liver with a blood vessel placed perpendicular to the axis of the transducer and near the focus. This approach follows recent work by the authors [Curra et al., IEEE Trans. Ultrason. Ferroelectr., Freq. Control (in press)]. Simulations are presented for different levels of driving pressure, sound nonlinearities, exposure times, and the relative position between the transducer focus and the blood vessel. [Work supported in part by DARPA and the CRDF Cooperative Grants Program.]
Intensity discrimination of brief Gaussian-windowed tones by hearing-impaired listeners
Authors: Baer Thomas , Moore Brian C. J. , Marriage Josephine
Published: July 2002

For normal listeners, intensity DLs for Gaussian-shaped tone pulses are largest at medium pulse durations when the pedestals are 10 dB above threshold, either in quiet or in a pink-noise background. One explanation is that worst performance occurs when the internal representation is most compact in time and frequency, affording minimal opportunity for multiple looks [N. H. van Schijndel, T. Houtgast, and J. Festen, J. Acoust. Soc. Am. 105, 3425–3435 (1999)]. However, the mid-duration worsening is largest for medium overall levels, suggesting an involvement of the compression on the basilar membrane (BM), which is also greatest at medium levels [T. Baer, B. C. J. Moore, and B. R. Glasberg, J. Acoust. Soc. Am. 106, 1907–1916 (1999)]. If so, the mid-duration worsening should be reduced when BM compression is reduced by outer hair cell damage. To test this, subjects with sensorineural losses were tested using 1-kHz or 4-kHz pulses, in quiet or in pink noise that raised thresholds by 10–20 dB. For subjects with mild losses, poorest performance was sometimes found for medium durations. For more severe losses, intensity DLs tended to improve monotonically or remain roughly constant with increasing duration. The results provide support for both multiple-look and BM-compression explanations. [Work supported by MRC.]