bluuebunny/crossref_metadata_2025 huggingface dataset:
Heard Island Feasibility Test: Long-range sound transmission from Heard Island to Krylov underwater mountain
Authors: Burenkov S. V. , Gavrilov A. N. , Uporin A. Y. , Furduev A. V.
Published: October 2005

The Russian research vessel Akademik Nikolai Andreyev participated in the HIFT experiment while anchored above the Krylov Seamount (17.5° N, 30° W). The propagation path length from Heard Island to Krylov was 12.5 Mm, and was located just between the Ascension station (9 Mm) and the more distant American and Canadian stations (16 to 17 Mm). All 35 successful transmissions were received by two omnidirectional hydrophones and a 30-m-long array. Receptions were sampled at 228 Hz and processed in both time and frequency domains. The main result of the processing was quite unexpected: the signal exhibited strong amplitude variability (fading as deep as 20 dB in less than 5 min) and simultaneously exhibited an incredible phase stability. All the phase variance up to the accuracy of positioning was due to the mutual motion of the transmit and receive ships. The minimal propagation loss for cw transmissions was 120 dB. M-sequence processing indicated an 18- to 20-s arrival spread estimate. However, the arrivals were very unstable with a lifetime of about 5 min.
Heard Island signals through the Agulhas retroflection region
Authors: Brundrit G. B. , Krige L.
Published: October 2005

Heard Island Feasibility Test sound transmissions were received at sea some 300 km southwest of the Cape of Good Hope on a four-hydrophone vertical array deployed from the vessel SAS Umzimkulu. This area, 53-min travel time along the Atlantic path from Heard Island, lay immediately down path from strong regional variability in the acoustic properties of the SOFAR channel, associated with the retroflection of the Agulhas current. Many transmissions were not received at all whilst the four successful recordings exhibited a relatively high transmission loss. It appears that interaction between a warm water Agulhas ring and the local seamount bathymetry may have been responsible for the deterioration in the HIFT signal received off Cape Town and at other sites further along the Atlantic path. Nevertheless, the overall quality of these received signals with respect to phase stability and intensity was sufficient for the standard HIFT signal processing to be carried out.
Relative abundance and behavior of marine mammals exposed to transmissions from the Heard Island Feasibility Test
Authors: Bowles Ann E. , Smultea Mari , Würsig Bernd , DeMaster Douglas P. , Palka Debra
Published: October 2005

The Heard Island Feasibility Test source transmitted a hum at 209–220 dB re: 1 μPa at 175-m depth, centered on 57 Hz with a maximum bandwidth of 30 Hz for 1 h of every 3. Experienced marine mammal observers conducted line-transect surveys and monitored marine mammal behavior visually and acoustically in a 70×70 km square centered on the transmission site. Thirty-nine groups of cetaceans and 19 of pinnipeds were sighted from both vessels before the start of transmissions. Thirty-nine groups of cetaceans and 23 of pinnipeds were sighted during transmissions. Blue (Balaenoptera musculus), fin (B. physalus), and sperm (Physeter macrocephalus) whales were sighted during the base line period; blue, sperm, and possibly sei (B. borealis) whales were sighted during the transmission period. More schools of hourglass dolphins (Lagenorhynchus cruciger) were sighted during transmissions, but fewer groups of pilot whales (Globicephala melas), southern bottlenose whales (Hyperoodon planifrons), and minke whales (B. acutorostrata). The density of all cetaceans was 0.0157 groups/km2 before the transmissions and 0.0166 groups/km2 during. Antarctic fur seals (Arctocephalus gazella) and southern elephant seals (Mirounga leonina) were seen, but not in sufficient numbers to estimate abundance. One blue whale tracked before, during and after a transmission changed respiration and reorientation rates, but did not avoid the source detectably. Sperm whales and pilot whales were heard in 23% of 1181 min of baseline acoustic surveys; but in none of 1939 min during the transmission period. Both species were heard within 48 h after the end of the test.
Green’s functions for wave propagation above an impedance ground
Authors: Li Y. L. , White Michael J. , Hwang M. H.
Published: October 2005

In this paper, a new method is introduced for attacking the problem of sound propagation above an impedance ground. This new method is based on a technique in which the solution of the Helmholtz equation is expressed as a onefold integral with an integrand that is identified as the solution of the heat conduction equation for an auxiliary problem. The heat conduction equation is solved via the inverse Laplace transform and its solution is substituted back into the original onefold integral. Finally, the new integral solution of the Helmholtz equation is approximated by the modified stationary phase method. Solutions of the Helmholtz equation are given for point and line sources above an impedance ground. The results obtained from these new solutions are compared with results from direct numerical integration of the exact solution. The agreement is excellent.
Considerations in bond strength evaluation by ultrasonic guided waves
Authors: Singher Liviu , Segal Yitzhak , Segal Emanuel , Shamir Joseph
Published: October 2005

Acoustic wave propagation in a three-layer waveguiding configuration is analyzed. Considering an adhesive layer as a waveguide structure, it is shown that the propagation of guided modes is affected by the bonding quality. A comprehensive study demonstrates the possibility of utilizing measurements on guided wave propagation to detect interfacial weakness between an adhesive and adherend.
Caustics and beam displacements due to the reflection of spherical waves from a layered half-space
Authors: Ainslie Michael A.
Published: October 2005

The pressure field due to the reflection of spherical waves from a layered half-space is examined. Beam displacements are calculated for various sound-speed and density profiles, with or without a step change, with particular attention to the resulting caustics and associated phase shifts. It is demonstrated that (for an e−iωt time dependence) the phase shift arising through such a caustic is always −π/2, regardless of whether caused by continuous refraction or by reflection with beam displacement. It is also shown that the beam displacement (and hence the reflected field) arising from a class of sech-squared density profiles is identical to that due to a step change in sound speed.
Increased incoherent backscattering from a liquid–solid interface at the Rayleigh angle
Authors: Nagy Peter B. , Adler Laszlo
Published: October 2005

The experimentally observed peak in the backward radiation from a liquid–solid interface at the Rayleigh angle is caused by a sharp increase in the otherwise relatively weak incoherent scattering from the inherent inhomogeneities of the solid. The increase of the incoherent backscattering is essentially a specular effect in contrast with the nonspecular, finite-beam effect predicted to cause the much weaker coherent reflection. The incoherent scattering can be caused by either geometrical irregularity or material inhomogeneity (e.g., surface roughness or polycrystalline grain structure). This paper presents analytical results showing that, regardless of the physical nature of the scattering inhomogeneity, there is a distinct peak in the backscattered intensity around the Rayleigh angle. The angular dependence of the incoherent backscattering is determined by the average properties of the liquid and the solid. The peak always occurs at the Rayleigh angle and the width of the peak is determined by the density ratio between the solid and the liquid. The maximum backscattering at the peak is essentially independent of the average material properties and is determined solely by the scattering inhomogeneity.
Measurements of the vibrato rate of ten singers
Authors: Prame Eric
Published: October 2005

The vibrato rate for ten singers, all singing Schubert’s Ave Maria, was measured on sonograms. Commercially available CD records were used to insure that the vibrato originated in a real musical performance. It was found, that the vibrato rate typically increased at the end of each tone, +15% in average, while no typical structure could be found in the beginning of a tone. Disregarding the increase of vibrato rate toward tone endings, the mean rate across singers was 6.0 Hz. The average variation between maximum and minimum rate within an artist is about ±8% of the artist’s average.
Measurements of some parameters of bowing
Authors: Schumacher Robert T.
Published: October 2005

The maximum bow force for Helmholtz oscillations, and the frequency shift as a function of bow force, have been measured for unstopped notes on a variety of violin strings. A bowing machine is briefly described on which data using bowing velocities at 5 and 10 cm/s were obtained. Computer simulations using the standard friction function model of the bowed string were also done. The combination of the measurements and the simulations allow an assessment of the probable validity of the friction curve model of the force between bow hair and string in bowed string motion.
Dynamics of the pianoforte string and narrow hammers
Authors: Zhu W. D. , Mote C. D.
Published: October 2005

A new method of solution to the equation of a perfectly flexible string, when struck at any point by hard or soft narrow hammers, is developed. The hard hammer is modeled as a point mass, and the soft hammer is modeled as a point mass backed by a linear or nonlinear spring and a dashpot, representing the compliance and dissipation of the felt. For each hammer the equation describing the string–hammer contact force during the periods of contact, and of recontacts, is derived explicitly. The Green’s function for a fixed-fixed string is represented by an infinite series of Heaviside functions. The analysis is exact in the spatial domain thereby eliminating modal truncation error and capturing all discontinuities in the contact force. The method predicts the contact force and system response under impacts given any hammer to string mass ratio that experiences any number of multiple contacts during the hammer strike.
On the perceptual strength of prosodic boundaries and its relation to suprasegmental cues
Authors: de Pijper Jan Roelof , Sanderman Angelien A.
Published: October 2005

A speaker structures utterances very clearly by grouping words into phrases. This facilitates the listener’s recovery of the meaning of the utterance and the speaker’s intention. To this purpose, a speaker uses, among other things, suprasegmental cues, such as intonation, pauses and prefinal lengthening of speech sounds. The research described here is concerned with the relationship between the strength of prosodic boundaries in spoken utterances as perceived by untrained listeners (perceptual boundary strength, PBS) and the phonetic cues melodic discontinuity, pause, declination reset and, to a limited extent, prefinal lengthening. The results indicate that untrained listeners can give reliable and usable judgments of PBS and that this is true even if the lexical contents of the utterances is made unrecognizable, thus blocking access to lexical, syntactic, and semantic information. There is a clear relation between PBS and the phonetic cues, the general trend being for PBS values to increase as more phonetic cues are associated with a given word boundary. The experimentally obtained PBS values were also compared with boundaries predicted on the basis of a syntactic and metrical analysis of the material. A high agreement was found between the PBS values found and the theoretically predicted prosodic structure.
Low-pass filtering in amplitude modulation detection associated with vowel and consonant identification in subjects with cochlear implants
Authors: Cazals Yves , Pelizzone Marco , Saudan Olivier , Boex Colette
Published: October 2005

Temporal auditory analysis of acoustic events in various frequency channels is influenced by the ability to detect amplitude modulations which for normal hearing involves low-pass filtering with a cutoff frequency around 100 Hz and a rejection slope of about 10 dB per decade. These characteristics were established in previous studies measuring modulation transfer functions. For cochlear implant subjects, the delivery of detailed amplitude modulation information has been recently shown to result in very significant improvements in speech understanding. Several previous studies on cochlear implant subjects have reported capacities for temporal resolution rather equivalent to those of normally hearing subjects but with some notable individual differences. Recently two studies on some cochlear implant subjects indicated modulation transfer functions often quite similar to those of normal hearing but exhibiting marked individual differences in shape and absolute sensitivity. The present study compared amplitude modulation detection and phonetic recognition in a group of cochlear implant subjects to determine the extent to which the two tasks are correlated. Nine individuals who had been implanted with an Ineraid device and who demonstrated open speech understanding ranging from excellent to poor were chosen and tested in the present study. For each subject modulation transfer functions were measured at the most apical electrode and phonetic recognition of isolated vowels and intervocalic consonants was assessed. Results showed a strong correlation between the depth of high-frequency rejection in modulation transfer functions and success in vowel and consonant intelligibility. These results emphasize the importance of temporal speech features and offer perspectives for customizing signal processing in cochlear implants.
The perception of speech sounds recorded within the uterus of a pregnant sheep
Authors: Griffiths Scott K. , Brown W. S. , Gerhardt Kenneth J. , Abrams Robert M. , Morris Richard J.
Published: October 2005

The intelligibility of speech stimuli recorded within the uterus of a pregnant sheep was determined perceptually using a group of untrained judges. The intrauterine sound environment of the ewe was intended to simulate that of a pregnant woman. Two separate lists, one of meaningful and one of nonmeaningful speech stimuli, were delivered through a loudspeaker to the side of the ewe and were simultaneously recorded with an air microphone located 15 cm from the flank and with a hydrophone previously sutured to the neck of the fetus. Perceptual test tapes generated from these recordings were played to 102 judges. The intelligibility of the phonemes recorded in the air was significantly greater than the intelligibility of phonemes recorded from the uterus. A male talker’s voice was more intelligible than a female talker’s voice when recorded from within the uterus, but not so when recorded in the air. An analysis of the feature information transmission from recordings inside and outside the uterus revealed that voicing information is better transmitted in utero than place or manner information.
Melodic cues to the perceived ‘‘finality’’ of utterances
Authors: Swerts Marc , Bouwhuis Don G. , Collier René
Published: October 2005

One of the possible functions of intonation is its capacity to clarify textual structure. It may indicate, for instance, that a sentence is likely to be the last one in a sequence of statements that build a discourse unit. In order to investigate the perception of melodic cues to ‘‘finality,’’ a series of three listening experiments was performed with short sentences, the intonation of which was manipulated with respect to different melodic variables. The actual testing was done in two ways (1) by pairwise comparison and (2) by absolute rating. A linear least-squares estimation method brought to light that in both tests finality judgments were influenced significantly by differences in pitch register (experiment 1), pitch range (experiment 1), and shape of the pitch contour (experiments 1, 2, and 3). The results of the data analysis suggest strongly that these different variables generally combine additively in producing finality judgments, though the effect of one is sometimes conditional on the value of another.
Morphological and acoustical analysis of the nasal and the paranasal cavities
Authors: Dang Jianwu , Honda Kiyoshi , Suzuki Hisayoshi
Published: October 2005

Morphological measurements of the nasal and paranasal cavities were conducted to investigate their relevance to the acoustic properties of the human nasal tract. The magnetic resonance imaging (MRI) technique was used to measure the three-dimensional geometry of the vocal tract. The area function of the nasal tract was calculated for seven subjects based on data obtained during natural breathing. The entire vocal tract was measured for five subjects during sustained production of nasal consonants. A marked morphological difference was observed between our data and previously published data [A. S. House and K. N. Stevens, J. Speech Hear. Disord. 21, 218–232 (1956); G. Fant, Acoustic Theory of Speech Production (Mouton, The Hague, 1970), 2nd ed., p. 139] particularly in the middle portion of the nasal tract. Previous data derived from cadaver specimens showed a large cavity in the middle portion possibly due to an absent or dehydrated mucous membrane, while our data showed narrow passages due to thickly layered mucosa. It has been confirmed by an additional experiment that the wide cavity is reproducible by applying an adrenergic agent to the nasal mucosa. Transfer functions of the vocal tract and the nasal tract were calculated from measured data, and compared to spectra of real speech signals recorded subsequent to the MRI experiment. The results indicate that asymmetry between the two nasal passages can cause extra pole-zero pairs, and suggest that the paranasal cavities play an important role in shaping the spectral characteristics of human nasal sounds.
An international comparison of long-term average speech spectra
Authors: Byrne Denis , Dillon Harvey , Tran Khanh , Arlinger Stig , Wilbraham Keith , Cox Robyn , Hagerman Bjorn , Hetu Raymond , Kei Joseph , Lui C. , Kiessling Jurgen , Kotby M. Nasser , Nasser Nasser H. A. , El Kholy Wafaa A. H. , Nakanishi Yasuko , Oyer Herbert , Powell Richard , Stephens Dafydd , Meredith Rhys , Sirimanna Tony , Tavartkiladze George , Frolenkov Gregory I. , Westerman Soren , Ludvigsen Carl
Published: October 2005

The long-term average speech spectrum (LTASS) and some dynamic characteristics of speech were determined for 12 languages: English (several dialects), Swedish, Danish, German, French (Canadian), Japanese, Cantonese, Mandarin, Russian, Welsh, Singhalese, and Vietnamese. The LTASS only was also measured for Arabic. Speech samples (18) were recorded, using standardized equipment and procedures, in 15 localities for (usually) ten male and ten female talkers. All analyses were conducted at the National Acoustic Laboratories, Sydney. The LTASS was similar for all languages although there were many statistically significant differences. Such differences were small and not always consistent for male and female samples of the same language. For one-third octave bands of speech, the maximum short-term rms level was 10 dB above the maximum long-term rms level, consistent across languages and frequency. A ‘‘universal’’ LTASS is suggested as being applicable, across languages, for many purposes including use in hearing aid prescription procedures and in the Articulation Index.
Forward- and backward-masked intensity discrimination measured using forced-choice and adjustment procedures
Authors: Turner Christopher W. , Horwitz Amy R. , Souza Pamela E.
Published: October 2005

A ‘‘midlevel’’ hump in the intensity jnd has been reported for pure tones preceded [e.g., Zeng et al., Hear. Res. 55, 223–230 (1991)] or followed [Plack and Viemeister, J. Acoust. Soc. Am. 92, 3097–3101 (1992)] by an intense masker where the signal-masker interval was 100 ms. These previous studies used forced-choice procedures, in which subjects were required to indicate the more intense tone. Plack and Viemeister [J. Acoust. Soc. Am. 92, 3097–3101 (1992)] have proposed that the task of judging the intensity of the short probe tone, when it is presented along with an intense masker, may lead to cognitive or central factors influencing the results. The present experiments attempted to reduce these possible effects by measuring intensity jnd’s using two additional paradigms. First, a ‘‘multiple-look’’ forced-choice method, in which subjects listened to the stimulus pairs several times before responding, was used to obtain only forward-masked intensity jnd’s. Second, the method of adjustment was used to obtain both forward- and backward-masked intensity jnd’s. Both the standard forced-choice method and the multiple-look forced-choice method yielded jnd data with a midlevel hump, when compared to jnd’s measured without a masker. In contrast, jnd’s obtained with the method of adjustment yielded jnd data with no midlevel hump. The present results suggest that the traditional method of adjustment for intensity discrimination, where subjects adjust the signal level to a point of subjective equality, may measure a fundamentally different quantity than that measured by forced-choice procedures.
Amplitude modulation rate discrimination with sinusoidal carriers
Authors: Lee Jungmee
Published: October 2005

Discrimination of the change in rate of sinusoidal amplitude modulation was investigated for sinusoidal carriers. The just-noticeable change in the modulation rate was measured as a function of (1) carrier frequency (fc=500, 1000, 2000, or 4000 Hz), (2) initial modulation rate (fm=10, 20, 40, 80, 160, or 320 Hz), and (3) stimulus duration (T=62, 125, 250, 500, 1000, or 2000 ms). For modulation rates less than 320 Hz, the thresholds for a change in modulation rate were not affected by changing the carrier frequency. When fm=320 Hz, the threshold for changes in the modulation rate ordered in the same way as the threshold for changes in the frequency of a pure tone, suggesting that the primary cue for discriminating a change in modulation rate was the frequency of either sideband. As stimulus duration increased to a certain T (critical duration), the thresholds decreased by more than a factor of 2. Above that duration, the thresholds for changes in modulation rate decreased only slightly or remained constant. The critical duration corresponded to about five cycles of modulation, at least for the slower modulation rates.
Time harmonic acoustic Bloch wave propagation in periodic waveguides. Part I. Theory
Authors: Bradley C. E.
Published: October 2005

The propagation of linear, dissipative, time-harmonic acoustic waves in a broad class of periodic waveguides is investigated theoretically. It is shown that a Floquet-like theorem is applicable to the system of partial differential equations and boundary conditions that describes the dynamics of a thermoviscous fluid in a periodic waveguide, and that the solution wave functions are therefore Bloch wave functions. Expressions for the parameters that characterize the Bloch wave functions are derived and the band structure of these functions of frequency is investigated. It is found that conditions of axial inversion symmetry (the waveguide may be isotropic or anisotropic) and reciprocity impose substantial restrictions on the allowed Bloch wave solutions.
Time-domain experiments on the diffraction of sound by a step discontinuity
Authors: Chambers James P. , Berthelot Yves H.
Published: October 2005

Experiments have been conducted to study the propagation of sound over a rigid surface with a step discontinuity. The Biot–Tolstoy–Medwin (BTM) model of a rigid wedge [J. Acoust. Soc. Am. 69, 1060–1064 (1981)] is used to predict the acoustic field directly in the time domain. Experiments carried out with a transient acoustic spark source confirm that: (1) in the region where there are no direct reflected waves, diffracted waves combine with diffracted/reflected waves to produce a smooth transition; (2) the acoustic field around the step discontinuity can be highly directional due to the interference of the direct, the reflected, the diffracted, and the diffracted/reflected waves; and (3) the acoustic field is essentially unchanged if the step discontinuity is replaced with a smooth step whose radius of curvature is less than the characteristic wavelength of the incident sound.
Leaky waves on curved scatterers. I. Fresnel width of coupling regions and elliptical Fresnel patches
Authors: Marston Philip L.
Published: October 2005

A common procedure for estimating the apparent width of a ray in volume propagation is to construct the locus of defective paths having a phase shift that deviates from that of the true ray by π radians [Yu A. Kravtsov and Yu I. Orlov, Sov. Phys. Uspekhi 23, 750–760 (1980); P. L. Marston, Phys. Acoust. 21, 1–234 (1992)]. An analogous construction is described for the effective surface region for the high-frequency coupling of sound with a leaky wave on a curved surface along a given ray. Results are shown for right circular cylinders and spheres. For defective paths in the plane of incidence of the ray, the resulting Fresnel angular half-width of the patch is approximately [2π/(ka cos θl)]1/2 radians where a is the radius of the surface, sin θl=c/cl and cl is the leaky wave phase velocity. The analysis is relevant to estimating the degree to which ray coupling processes can be considered to be local processes. It is also relevant to the anticipation of the transition to creeping wave behavior when cl becomes sufficiently small for the Fresnel region to touch the edge of the scatterer. Defective paths outside the plane of incidence are also considered for a right circular cylinder. The Fresnel patch associated with a leaky ray to (or from) a specified point on the cylinder is approximately elliptical and the analysis is relevant to radiation as well as to scattering.
Noise reduction for hearing aids: Combining directional microphones with an adaptive beamformer
Authors: Kompis Martin , Dillier Norbert
Published: October 2005

Many hearing aid users complain about a reduced intelligibility of speech in noisy environments. Directional systems are a successful approach for noise reductions in hearing aids. These systems transmit signals from acoustic sources lying in front of the hearing aid user while suppressing signals from other directions, which are assumed to be noise. Several methods are known to obtain directivity. One is to use directional microphones, another is digital postprocessing of several microphone signals. In this letter, the combination of directional microphones with the adaptive beamformer, a directional signal processing approach, is discussed. Intelligibility tests with both normal-hearing and hearing-impaired subjects are presented. It is shown that the combination of directional microphones with digital postprocessing is able to improve the intelligibility of speech in a noisy environment significantly, when compared to any one of these two approaches by itself.
Adiabatic modes for a point source in a plane-geometry ocean
Authors: Porter Michael B.
Published: October 2005

The adiabatic-mode solution is widely used for modeling sound propagation in slowly varying ocean environments. However, there are several variations of adiabatic mode solutions and there has been confusion about which form is correct. The standard derivation yields a form that is not reciprocal. As such, it has often been modified in an ad hoc fashion to produce a form that is reciprocal. This lack of reciprocity is due to the common assumption that the environment is rotationally symmetric about the source. By assuming instead a plane-geometry environment a new adiabatic form that is reciprocal is derived.
Towards understanding the limits of distortion product otoacoustic emission measurements
Authors: Gorga Michael P. , Neely Stephen T. , Bergman Brenda M. , Beauchaine Kathryn L. , Kaminski Jan R. , Liu Z.
Published: October 2005

Distortion product otoacoustic emission (DPOAE) data were obtained with a custom-designed system from 20 subjects with normal hearing. Cavity measurements, using this system and an Etymotic ER-10B low−noise microphone system, resulted in estimates of recording system distortion of −20 dB SPL for f2 frequencies ranging from 500 to 8000 Hz, and primary levels ranging from 20 to 75 dB SPL (L2=L1−10 dB). Using this system it was possible to automatically adjust averaging time in order to obtain the same residual noise levels across frequencies. In all subjects with normal hearing, DPOAEs were measurable over a wide range of primary levels for octave f2 frequencies from 1000 to 8000 Hz, but not at 500 Hz. At 500 Hz, only half of the normal−hearing subjects produced DPOAEs that were above the noise floor. When they did, DPOAE amplitude was less than that observed at higher f2 frequencies. While the cause for response absence in some normal ears may have been due to residual noise, the reduced amplitude suggests that the other factors influence the measurement of DPOAEs at low frequencies. This result may be due to reduced cochlear production of DPOAEs at lower frequencies or reduced transmission through the middle ear.
A computational model with ionic conductances for the fusiform cell of the dorsal cochlear nucleus
Authors: Kim D. O. , Ghoshal S. , Khant S. L. , Parham K.
Published: October 2005

A computational model of a fusiform cell of the dorsal cochlear nucleus was developed. The results of model simulations are compared with the results of in vitro experimental observations obtained by other investigators. The structure of the present model is similar to that of Hodgkin–Huxley [J. Physiol. 117, 500–544 (1952)]. The model incorporates five nonlinear voltage-dependent conductances (three potassium and two sodium types) and their associated equilibrium-potential batteries, a leakage conductance, the membrane capacitance, and a current source. Model responses were obtained under both current- and voltage-clamp conditions. When a hyper- and depolarizing current sequence was applied [Manis, J. Neurosci. 10, 2338–2351 (1990)], the cell model was able to reproduce builduplike and pauserlike discharge patterns closely resembling Manis’ observations. A transient ‘‘A’’-type potassium conductance in the model played a major role in generating this phenomenon. The model predicts that blocking the ‘‘A’’ conductance should convert a builduplike or pauserlike pattern into a sustained regular pattern. A persistent sodium conductance in the model played the main role in reproducing: Spontaneous regular discharges; a discharge after a long latency under a long small (+0.025 nA) current; and nonlinear voltage–current characteristics with positive currents. Usefulness of the model can be seen as follows: (1) Several sets of experimental observations can be integrated into a common framework; (2) possible roles of different ionic conductances postulated to be present in the cell can be inferred by observing the model behavior with the conductances intact or blocked; and (3) time courses of ionic currents and conductance values obtained from the model under current- and voltage-clamp conditions can serve as predictions to be tested in future experimental studies.
Active noise control in ducts via side-branch resonators
Authors: Okamoto Yasushi , Bodén Hans , Åbom Mats
Published: October 2005

This paper discusses active noise control in ducts via side-branch resonators. A general analysis of the problem is given together with a detailed study of the case of an active straight pipe resonator. The analysis focuses on how to minimize the secondary source strength (volume velocity) necessary for active control. The main conclusion is that, by using a resonator with an end-mounted high impedance secondary source, it is possible to reduce the required source strength compared to the case with the secondary source directly mounted on the duct wall. This is important for applications on machines that generate very high sound levels, e.g., compressors and IC engines. The result from an experimental test of an ‘‘active quarter wavelength resonator’’ is also presented. This test verifies that a large reduction in the necessary secondary source strength is achieved at and around the resonators resonance frequencies.
Measurements of nonlinear effects in a driven vibrating wire
Authors: Hanson Roger J. , Anderson James M. , Macomber H. Kent
Published: October 2005

Experimental measurements have been made of the motion of a red brass harpsichord wire driven electromagnetically in a fixed direction perpendicular to the equilibrium position of the wire. The motion is complex compared to that predicted by simple linear theory because of effects due to tensional changes and longitudinal motions. Optoelectronic detectors are used to measure amplitude and phase of the transverse motions as functions of the driving frequency, both in the driving direction y and the direction z perpendicular to y. Near the free-vibration fundamental frequency f0 the z and y amplitudes are comparable even for a very low driving force and amplitude. Amplitude jumps and hysteresis effects are observed for large amplitudes. The z–y phase difference is measured as 0°, 90°, and 180° in different frequency regions, yielding both planar and whirling or tubular motion. As the driving frequency increases, the phase difference between the driving force and the y motion varies steadily from 0° to 90° before jumping to 180°. There is no evidence of a critical frequency of onset of the z motion as is predicted in some theoretical treatments. Similar effects are observed near 3f0, for which amplitude measurements have been made down to 0.01 μm for a 0.71-m-long wire.
Vortex structural power flow in a thin plate and the influence on the acoustic field
Authors: Tanaka Nobuo , Snyder Scott D. , Kikushima Yoshihiro , Kuroda Masaharu
Published: October 2005

This article examines the characteristics of real vibrational power flow in a simply supported rectangular panel under the action of feedforward vibration control, induced by a control source input which is slightly suboptimal such that the primary source is producing a slight amount of real vibrational power, and the control source is absorbing the same amount. It is found that the path of the power flow is a combination of translations and rotations, the rotations induced by the interference of two modes which produces a ‘‘vortex generating block.’’ A qualitative formula for predicting the number of power flow vortices, as well as the discussion of the vortex period, is put forward. A novel method to induce a vortex at an arbitrary location of the plate is also shown, which may have practical applications in controlling the path of vibrational power flow in systems of large extent. Moreover, the influence of the induced vortex power flow on the plate onto the acoustic intensity distribution is investigated, showing that the rotational direction of the vortex on the plate is not always the same with that of the acoustic intensity in the near field.
Dynamic analysis of piezoelectric actuator-driven circular rings using an impedance approach
Authors: Rossi Anna , Liang Chen , Rogers Craig A.
Published: October 2005

This paper presents a dynamic model for the response of a circular ring excited by piezoelectric transducer (PZT) actuators bonded on the ring surface. The dynamic response is determined based on the dynamic interaction between the PZT actuators and the structure using an impedance approach. Compared with the conventional static approach, in which a statically determined ‘‘equivalent force’’ of the actuator is used as the forcing function in the dynamic analysis, the impedance approach cannot only capture the physics of the actuator/structure interaction, but also accurately predict the structural dynamic response. Experiments have also been conducted to verify the theoretical model. The predicted dynamic response using the impedance approach agrees very well with the experimental results. Comparison of the conventional static approach and the impedance model has also been presented.
Modeling of distributed piezoelectric actuators integrated with thin cylindrical shells
Authors: Zhou Su-Wei , Liang Chen , Rogers Craig A.
Published: October 2005

The dynamic interaction between induced strain piezoelectric (PZT) actuators and their host structures is often ignored in the modeling of intelligent structures. A more realistic investigation of intelligent material systems must account for the dynamic behaviors of integrated actuator/substrate systems. In this paper, a generic method for the dynamic modeling of distributed PZT actuator-driven thin cylindrical shells has been developed using a mechanical impedance approach. The impedance characteristics of a cylinder corresponding to the excitation of a pair of pure bending moments have been developed, from which the dynamic output moments (or forces) of PZT actuators can be accurately predicted. Direct comparisons have been made between a conventional static modeling approach and the impedance method in order to identify the critical differences between these modeling methods for thin cylindrical structures. The case studies demonstrate that the mechanical impedance matching between PZT actuators and host structures has an impact on the output performance of the actuators. The dynamic essence of integrated PZT/substrate systems has thus been revealed.
Double layer actuator
Authors: Photiadis Douglas M. , Bucaro Joseph A. , Corsaro Robert D.
Published: October 2005

This paper examines the potential for dual-layer actuators to achieve radiation efficiencies independent of the backing structure. It presents a simple center-of-mass representation for the device, and uses it to describe the kinematics of the dual layer actuator system with the purpose of identifying broad guidelines regarding thickness and frequency range issues. This approach has the advantage of providing a direct physical view of the device operation. In this context, it is shown that these devices work by electrically moving the center of mass of the transducer in opposition to the motion of the adjoining fluid. While such devices are shown to be generally less efficient than the simple parallel-driven double-layer transducer, over much of their operating range the loss in efficiency is found to be only a few decibels.
The three-dimensional equivalent circuit and the natural frequencies of rectangular piezoelectric ceramic resonators
Authors: Shuyu Lin
Published: October 2005

The three-dimensional coupled vibration of the piezoelectric ceramic resonator is analyzed when the shearing stress and strain are ignored. Three mechanical coupling coefficients are introduced and the coupled vibration is reduced to three equivalent one-dimensional extensional vibrations. On the basis of the analysis, the three-dimensional equivalent circuit is derived. From the equivalent circuit, it can be seen that as the three equivalent one-dimensional vibrations are coupled to each other, a new kind of electromechanical transformation force arises in the circuit. The natural frequency equation is derived and the natural frequencies of some rectangular piezoelectric ceramic resonators are computed. As the mechanical coupling between the vibrations in different directions and the piezoelectric effect are considered, the computed resonance frequencies are in good agreement with the measured results.
Ultrasonic measurements in polymeric materials using air-coupled capacitance transducers
Authors: Hutchins David A. , Wright William M. D. , Schindel David W.
Published: October 2005

Wide bandwidth capacitance devices have been designed which have a high transduction efficiency in air at frequencies into the MHz range. They are sufficiently sensitive to allow transmission through solid samples, including polymers and fiber-reinforced composites. Examples are presented of experiments showing how such transducers may be used to measure material properties and to perform ultrasonic imaging.
An investigation of the accuracy of oblique incidence ultrasonic reflection coefficient measurements
Authors: Pialucha Tom , Cawley Peter
Published: October 2005

An investigation of the accuracy of ultrasonic reflection coefficient measurements from layered structures at oblique incidence is described. The measured reflection coefficients from a series of interfaces are compared with the predictions of a plane-wave (infinite transducer) model, and with predictions taking into account the finite size of the transducers. It has been shown that experiments with finite-sized transducers can be used to measure the plane-wave reflection coefficients from any interface within the system, provided that the angle of incidence is remote from any critical angle of the system, and that the receiver is placed at the center of the area insonified by the reflection of interest. If quantitative predictions of the full response measured by the real transducers are to be obtained, or if predictions at angles of incidence close to any critical angles are required, then finite transducer theory must be used. The reflection coefficients measured using a pair of 10-MHz center frequency, broadband transducers agreed with the theoretical predictions to within ±3% when the reflection coefficient from the top surface of a plate system was measured, and to within ±5% when an embedded interface was considered. The reproducibility of the measurements was found to be as good as ±1% provided that great care was taken in aligning the transducers when the rig was set up.
High-frequency forward scattering from Gaussian spectrum, pressure release, corrugated surfaces. I. Catastrophe theory modeling
Authors: Williams K. L. , Stroud J. S. , Marston P. L.
Published: October 2005

A high-frequency approximation is derived for forward scattering from Gaussian spectrum, pressure release, corrugated surfaces. The derivation uses ideas and results from catastrophe theory [M. V. Berry, Adv. Phys. 25, 1–26 (1976)] to include diffraction. The starting point is the Kirchhoff approximation for scattering from a rough surface. As a result of this analysis, the scattered pressure is written in terms of a finite set of diffraction catastrophes and stationary phase contributions. The high-frequency approximation is applied to forward scattering from a corrugated surface that is a single realization from a Gaussian spectrum population. The validity of the results is demonstrated in a comparison with numerical integration of the Helmholtz integral for this same surface. The physical insight that catastrophe theory supplies is demonstrated by dissecting the forward scattered pressure. This dissection separates the geometrical acoustics, diffractive, and interference contributions to the spatial structure of the scattered pressure. The high-frequency results are also used to calculate the pressure for short-tone bursts scattered from the surface. The scattered pressure consists of a series of pulse replicas, some of which are interfering. The region of the surface responsible for each pulse replica is determined, and the pulses classified, via the high-frequency approximation.
A normal mode theory of air-to-water sound transmission by a moving source
Authors: Kazandjian Luc , Leviandier Luc
Published: October 2005

This paper addresses the problem of evaluating the acoustic pressure field generated in the oceanic waveguide by a uniformly moving airborne source. The air, water, and seabed media are stationary and stratified. The pressure in the far field is obtained in terms of the normal modes usually utilized in underwater and aerial transmission loss calculation. The expression obtained is shown to be in accordance with specialized results found by other authors and is physically interpreted. The influence of the source movement on propagation loss is considered.
Solutions of coupled-mode equations with a large dimension in underwater acoustics
Authors: Knobles D. P.
Published: October 2005

A method is presented for the solution of coupled-mode equations for sound propagation in a range-dependent waveguide. By following a new approach recently introduced in nuclear theory, the coupled-mode equations are modified and then solved using the Lanczos method. Calculations are made for isovelocity waveguides with rigid bell-shaped bathymetries having large slopes. Convergence properties and computer CPU times are examined as a function of the dimension of the coupled-mode equations and the nature of the coupling. The efficiency of the approach is shown to increase as the dimension of the coupled-mode equations increases.
Observations of underwater sound from laboratory breaking waves and the implications concerning ambient noise in the ocean
Authors: Kolaini Ali R. , Crum Lawrence A.
Published: October 2005

The results of an experiment to characterize the underwater sound field radiated by various breaking waves intensities in fresh water in the range from 0.1 to 20 kHz are described. Waves are generated by a computer-controlled plunging-type wave maker and propagate along a 12.7-m-long channel where they are made to break at the mid-surface of a 3-×3-×2.5-m anechoic water tank. The individual bubbles and bubble clouds entrained by the breaking wave provide a mechanism for sound production. Using high-speed cinephotography, correlations were established between the hydrodynamic evolution of the cloud and the radiated acoustic emissions. The bubble size distributions inside the cloud were measured with the aid of a high-speed video camera and a fiber optic cable. These measurements indicate that single bubbles with radii as large as 7–8 mm may be entrained in this fresh-water system by moderate spilling breakers. Detailed measurements of the bubble size distribution of the bubble cloud enabled us also to obtain a measurement of the average void fraction in the cloud. These observations reveal that the sources of sound in laboratory spilling breakers is due mostly to single bubble oscillations that can have frequencies as low as 400 Hz; in the case of plunging breakers, it appears that both individual bubbles and bubble clouds can contribute to the acoustic emissions. The acoustic radiation from bubble clouds is the result of collective oscillations of the bubbles, stimulated by large scale vortices created by the plunging breaker. The sound spectra, averaged over 100 breakers, reveal the following observations. First, the peak frequencies of the average sound spectra shifts from few kHz (weak, spilling breaker) to few hundred Hz (plunging breaker). Second, the sound pressure levels increase in all frequency bands with increasing breaker severity. Lastly, the high-frequency portions of the sound spectra have slopes of about 5–6 dB/oct, which are the slopes observed for the noise spectra of the ocean. These results provide considerable insight into the likely source mechanisms for ocean ambient noise.
Broadband localization by matched fields in range and bearing in shallow water
Authors: Knobles D. P. , Mitchell S. K.
Published: October 2005

Data from a moving source received by three horizontally separated bottomed sensors in a shallow water environment are analyzed using a broadband matched-field approach to source localization. The water depth was approximately 150 m, and the low bottom loss in the area results in low spatial coherence of the broadband field. The modeled acoustic fields are constructed via a ray model. Localizations are made in the x-y plane. In a large search area the time evolution of the ambiguity surfaces produced from the data agree fairly well with simulated surfaces. Ambiguity surfaces are generated successively at intervals of about 1.6 s in small search areas with a fine spatial grid to test the possibility of tracking a source. Results of the source tracking are presented. The analysis also considers the effects of the sea floor on localization in the context of spatial coherence.