bluuebunny/crossref_metadata_2025 huggingface dataset:
Adaptation and recovery from adaptation in single fiber responses of the cat auditory nerve
Authors: Chimento Thomas C. , Schreiner Christoph E.
Published: October 2005

This study examined the time course of adaptation and recovery from adaptation of single auditory-nerve fiber responses. The conditions studied were: (1) adaptation response using low level, 800 Hz or characteristic frequency (CF) stimuli; and (2) onset recovery and whole tone response recovery of a probe tone following a masker of equal frequency with variable silent intervals between the masker offset and probe onset. Single unit responses to 290 ms long, 800 Hz or CF tones presented at 10–30 dB SL were recorded from the auditory nerve of the cat. Adaptation properties were determined and fit to the equation: A(tp)=Yre(−tp/τRr) +Yse(−tp/τRs)+Ass. Recovery from adaptation was determined by recording the response of a probe tone following a 100-ms masker tone equal in frequency to the probe, and with amplitudes ranging from 20- to 30-dB relative to the probe amplitude. Both the onset recovery and the whole tone recovery were determined for the single unit responses.

The onset data were analyzed and fit to either the equation: A(Δxt,tp)=Ass −Yre(−tp/τRr) −Yse(−Δt/τRs) or A(Δt,tp)=Ass−Yre(−Δt/τR). The whole tone response showed two distinctive time patterns that could be fit to either an adaptation equation or to the two-time-constant recovery equation, depending on the relative amplitude of the masker and the length of the silent interval between masker offset and probe onset. The results of this study indicate that single fiber time constants are comparable to those measured in previous studies using the auditory-nerve neurophonic (ANN). Likewise, the pattern of recovery of the whole tone response for single fiber responses is comparable to the ANN. Possible sites and mechanisms for adaptation and recovery from adaptation taking into account recent data from electrical stimulation studies and receptor channel morphology and kinetics are discussed.
A nonlinear least-squares technique for analyzing probability of detection data that uses all the data without grouping
Authors: Richter William Julius
Published: October 2005

The purpose of a probability of detection (PD) experiment is to quantify the ability of a system to detect signals embedded in noise. The first step in the classical technique for analyzing data from such an experiment is to least-squares fit the data to a Gaussian probability integral using Gaussian probability paper or probits such that the Gaussian probability integral plots as a straight line. Because of the ease with which data can be fitted to a straight line, the classical technique does not require a modern digital computer. The classical technique has been effective over the years in many applications, however its shortcomings are (1) groups of data points must exist at several signal to noise ratios (SNRs) with about the same number of data points at each SNR and (2) groups with SNRs where detections occur 100 or 0% cannot be used. Data must be regrouped or thrown out to meet these criteria. The nonlinear least-squares (NLLS) technique described in this paper avoids these problems by least squares fitting the data to a Gaussian probability integral directly. This is now possible with modern digital computers. NLLS allows each data point to be used independently as a sample probability of detection of 1 or 0. This avoids the need for data to be grouped at all and permits using all the data. Results are compared with the classical technique, and favorable agreement is attained where all the conditions of the classical technique apply. Examples where all these conditions are not present are also provided, and the advantage of the new technique is demonstrated. The analysis is performed with a program written in basic and run on a home computer. In applying the new technique to the examples, it was noted that errors in quantifying the ability of a system to detect signals can be large. Further analysis showed that the size of the errors depended on the location of the SNRs, and an iterative method is demonstrated for selecting SNRs such that reasonable accuracy is obtained with a small number (50) of data samples.
Acoustic scattering by a sound-hard rectangle
Authors: Boström Anders
Published: October 2005

The scattering of an incoming plane wave by a sound-hard infinitely thin rectangle is considered. Starting from a double spatial Fourier transform representation of the scattered wave, a matching of the conditions in the plane of the rectangle leads to an integral equation for the potential jump across the rectangle. This jump is expanded in a double series in Chebyshev polynomials which fulfill the right edge conditions (but no special measures are taken for the corners where the right conditions are anyway unknown). The integral equation is thus discretized and the only tricky part is the computations of the double integrals in the system matrix where special care must be exercised. A double stationary phase analysis gives the scattered far fields, and some numerical examples of total scattering cross sections are given.
Simulations of cochlear nucleus neural circuitry: Excitatory–inhibitory response-area types I–IV
Authors: Arle J. E. , Kim D. O.
Published: October 2005

Several circuitry schemes have been explored among model stellate and fusiform cochlear nucleus neurons in an effort to reproduce excitatory–inhibitory response-area (EIRA scheme) types I–IV. Single cell models incorporated known nonlinear membrane properties and spike-discharge characteristics, as described in previous modeling and intracellular recording. In addition, a unique method of implementing dendritic electrotonic distance processing was developed that provides greater computational efficiency, but with results similar to compartmental models. As an initial simple case, results were examined for a 5-kHz pure tone. Auditory nerve (AN) population responses across characteristic frequencies from 200 Hz to 50 kHz based on actual single unit recordings were incorporated into the model as input. The findings and conclusions are (1) relatively simple inhibitory connections among stellate and fusiform cells, all of which receive AN excitatory inputs, can account for the salient features of EIRA-scheme types I–IV; (2) both types III and IV may be obtained using fusiform cells with small adjustments in the anatomical connections; (3) if stellate cells laterally inhibit their own neighbors, they can create inhibitory sidebands, but may have difficulty avoiding multiple sidebands; (4) in the model, type II cells are not responsive to broadband noise but rather to pure tones, and the reason for this was partly because the type II cells were inhibited by other CN units, and partly because the simulated AN fiber response to broadband noise was near their threshold; and (5) the type IV complex response areas may actually arise not necessarily because of elaborate circuitry, but as a result of a complex AN fiber population profile at high stimulus levels in conjunction with the type II inhibitory input to the type IV cells.
Hearing loss from gun and railroad noise—Relations with ISO Standard 1999
Authors: Kryter Karl D.
Published: October 2005

Pure-tone hearing thresholds and anamnestic data pertaining to nosocusis and exposure to gun noise were analyzed for 9778 male railroad train-crew workers. A major portion of losses in hearing sensitivity due to railroad noise are obscured in comparisons of hearing levels of trainmen with the hearing levels of the unscreened samples of United States males given in Annex B, ISO 1999 [ISO 1999 (1990), ‘‘Acoustics—Determination of occupational noise exposure and estimation of noise-induced hearing impairment’’ (International Organization for Standardization, Geneva)]. Comparisons of the hearing levels, adjusted for nosocusis, of trainmen who had used no guns, with the hearing levels of otologically and noise screened males (Annex A, ISO 1999) reveal significant losses due to railroad noise. Additional losses were found at high frequencies in trainmen who had used guns. It appears that the effective Leq8h exposure level of trainmen to railroad noise is about 92 dBA, and 87–89 dBA to gun noise. These results are in general agreement with those of study of railway workers by Prosser et al. [Br. J. Audiol. 22, 85–91 (1988)]. Asymmetries in losses between the two ears, effects of ear protection, losses from nosocusis, and losses from sport, as compared to military, gun noise exposures, are examined.
Effects of nosocusis, and industrial and gun noise on hearing of U.S. adults
Authors: Kryter Karl D.
Published: October 2005

Hearing losses estimated for exposure to industrial and gun noise and for ‘‘typical’’ nosocusis are applied to the distributions of the hearing levels of adult males and females of the general population of an industrialized society unscreened for exposure to noise or ear disease. Noise exposure and demographic data applicable to the United States, and procedures for predicting noise-induced permanent threshold shift (NIPTS) and nosocusis, were used to account for some 8.7 dB of the 13.4 dB average difference between the hearing levels at high frequencies for otologically and noise screened versus unscreened male ears; (this average difference is for the average of the hearing levels at 3000, 4000, and 6000 Hz, average for the 10th, 50th, and 90th percentiles, and ages 20–65 years). According to the present calculations, this difference is due, in order of importance, to (1) nosocusis, (2) exposure to gun noise, and (3) exposure of workers to industrial noise. For these same frequencies and overall average, adjustments for nosocusis accounts for 2 dB of the 5.9-dB difference between the hearing levels of screened and unscreened female ears. For the average at 500, 1000, and 2000 Hz, the overall differences between the screened and unscreened populations is but 3.4 dB for males and 2.9 dB for females. The adjustment procedures reduced these differences to −0.5 and 0.9 dB, respectively.
A cylindrical resonator method for the investigation of low-frequency sound absorption in sea water
Authors: Qiu Xin-Fang
Published: October 2005

In this paper, a cylindrical resonator technique developed for the investigation of low-frequency sound absorption in sea water and synthetic media is described. The lowest usable measuring frequency has been extended down to about 3 kHz. Due to the low residual losses of the resonator system and to the high reproducibility of the energy decay time measurement, it was possible not only to measure excess absorption at normal sea water concentration and at low pH, but also, under certain conditions, to determine both the relaxation frequency and maximum absorption per wavelength of a single definite relaxation with acceptable accuracy, even though absorption was being measured mostly at two frequencies only. As examples, some experimental results are presented. An error analysis of the data is given.
Acoustic propagation through a turbulent atmosphere: Experimental characterization
Authors: Bass Henry E. , Bolen Lee N. , Raspet Richard , McBride Walton , Noble John
Published: October 2005

Experimental measurements of sound propagation through the atmosphere with particular emphasis on amplitude and phase fluctuations due to atmospheric turbulence are described. The experiment consisted of a source operated between 62.5 Hz and 8 kHz at heights of 1.5 and 30.5 m and an array of microphones 91.4–745 m from the source. The experimental site near Bondville, Illinois had good fetch and significant wind. The experimental acoustic propagation data is supplemented with meteorological measurements, including fluctuations in wind and temperature. The data has been analyzed in terms of the received amplitude and phase (relative to a reference microphone) forming a scatter plot in a complex plane, amplitude probability distribution, and transverse phase and amplitude structure functions. The scatter plot provides a qualitative measure of turbulence effects for applications requiring both phase and amplitude information. The amplitude probability distribution is more useful for noise estimates. The experimental structure functions are difficult to interpret at frequencies below 125 Hz due to the effects of background noise.
Methodology and programs for acoustic calculations of turbojet engine.
Authors: Zumtfort Boris S.
Published: October 2005

A methodology and associated programs have been created to calculate (1) a matrix of sound-pressure levels for fan (or ducted propfan), compressor, jet or jets, etc., and also turbojet, turbofan (TF), and TF with superlarge bypass ratio engines; (1a) the noise levels generated by aircraft in flight at various ground points; (1b) the area of the aircraft sound track (noise footprint); (2) optimum variant of balances for suppression of TF engine noise; and (3) optimum variant of tuning of the sound absorber liners considering the mass of the noise silencer. The results of these calculations are well confirmed by experimental data. This methodology can be also used on other applications: gas pumping stations, ships, etc.
Dimension-specific processing capacity for auditory patterns.
Authors: Kidd Gary R. , Watson Charles S.
Published: October 2005

Recent studies of complex auditory pattern discrimination have supported the hypothesis that, with novel patterns, the ability to resolve pattern details on a given dimension is affected by the amount of variation on that dimension [Watson etal., J. Acoust. Soc. Am. 88, 2631–2638 (1990)]. When the amount of variation on a dimension is very low, pattern discrimination is determined by absolute physical values (thresholds). However, when the amount of variation is high, discrimination is determined by the proportion of the pattern that is changed [C. S. Watson and G. R. Kidd, J. Acoust. Soc. Am. Suppl. 1 82, S40 (1987)]. This dimension-specific processing capacity hypothesis has been tested in experiments that measured threshold values of Δf/f for changes in a single target tone in nine-tone patterns. The amount of variation per dimension was manipulated in the frequency and temporal dimensions by including different numbers of frequencies and durations in the patterns. Three levels of variation per dimension were factorially combined to produce nine pattern-variation conditions. A considerable decrement has been found in frequency-discrimination performance with increases in the number of different frequencies, but little or no effect of increases in the number of different durations. Thus, at least under these conditions, listeners are only affected by changes in the amount of variation in tonal patterns when that variation is on the same dimension as the change to be discriminated. The conditions under which this dimension-specific limitation is expected to hold will be discussed. [Work supported by NIH with partial support from AFOSR to the Institute for the Study of Human Capabilities.]
Discriminability of correlated bursts of reproducible noise.
Authors: Fallon Susan M.
Published: October 2005

Discriminability of pairs of 100-ms bursts of noise was measured using a same–different psychophysical method. In the first condition, the correlation between bursts in a pair was fixed at 1.0 during each same trial. On each different trial, bursts were identical except for τ ms of independent noise located at either the beginning, the middle, or the end of the pairs. The correlation between bursts presented on each different trial was increased from 0.0 by decreasing the duration of τ. The second condition was the converse of the first; the correlation between bursts presented on each different trial was fixed at 0.0 and the correlation between bursts presented on each same trial was decreased from 1.0. As the τ ms of either the independent (condition 1) or the perfectly correlated (condition 2) noise is moved from the beginning to the end of the bursts, discriminability increases in the first condition and decreases in the second condition. These results suggest that a ‘‘difference’’ is a more salient cue in the discrimination task than a ‘‘sameness’’ and are discussed in terms of a correlational model. [Work supported by NIH and AFOSR.]
Testing fractal and multifractal concepts for seafloor topography.
Authors: Herzfeld Ute C.
Published: October 2005

Scattering and reverberation properties of the seafloor depend on the high-resolution spatial structure of submarine topography. Whether concepts of fractal geometry, scaling properties, and multifractal theory provide possibilities to describe the seafloor across several scales of resolution is investigated. In an attempt to predict the spatial structure of the seafloor beyond the scale resolved by survey systems, it has been proposed that the seafloor can be simulated using the self-similarity property of a fractal. (By definition, a fractal is an object of Hausdorff dimension strictly exceeding its topological dimension.) However, results from analyses of bathymetric data from the East Pacific Rise at 13° N/104° W and from the Juan de Fuca Ridge at 45° N/130° W show scale-dependent spatial structures, contradicting a simple self-similarity or self-affinity. Consequently, the seafloor probably has noninteger (fractal) dimension, but with different geologic processes dominating specific ranges of scale (rather than scale invariance). To capture the complexity of seafloor generating processes, the more versatile concept of multifractals is introduced and explored for seafloor topography description.
High-frequency forward scattering from the ice canopy: Experiment and comparison with specular point theory simulations.
Authors: Williams Kevin L. , Funk Dale E.
Published: October 2005

Acoustical forward scattering experiments were carried out in the spring of 1990 in the Beaufort Sea. Both 25- and 45-kHz tone bursts of 1- to 5-ms duration were used. A broad beamwidth four quadrant receiver and an omnidirectional source were employed in the experiment. The horizontal ranges between source and receiver for the results to be presented were 400–500 m. The receiver was 61 m below the arctic canopy and the sender depth was varied from 7 to 350 m. The canopy topography between the sender and receiver was profiled with an upward looking sonar. This allowed deterministic modeling of the forward scattered signal using specular point theory (SPT). Comparisons will be shown between individual experimental pings and SPT. The SPT based simulations reproduce the general characteristics of the experimental results in most cases. However, in certain geometries the surface topography is such that the approximations used in SPT are invalid. Examples of data/model comparisons for these geometries will be given. The physical reason for failure of SPT for these geometries will be shown to be due to the existence of random caustics. [Work supported by ONT with technical management by the Naval Coastal Systems Center (NCSC).]
Surface and bottom backscattering strengths measured from midrange reverberation in the CEAREX 89 arctic experiment.
Authors: Yang T. C. , Hayward Thomas J.
Published: October 2005

Acoustic reverberation data from SUS explosions collected during the CEAREX 89 experiment in the Norwegian–Greenland Seas are analyzed to estimate both under-ice and bottom backscattering strengths. Data from the 1230-m vertical array were previously used to measure scattering strengths from short-range (<3 km) under-ice reverberation returns [T. J. Hayward and T. C. Yang, J. Acoust. Soc. Am. 89, 1941 (A) (1991)]. The analysis here concentrates on midrange (up to 20 km) reverberation, and extracts the backscattering strengths from single and double bottom bounced data. The high-angle returns backscattered from the ice (and bottom) and specularly reflected from the bottom are recognized in the display of vertical-array beam response vs vertical arrival angle and time. Bottom losses are inferred from comparison of the single-bounce and double-bounce data using modeled transmission losses. This method provides both a larger scattering-area sample and higher incident/scattered angle backscattering strengths compared with the direct-path measurements. These results are compared with the short-range measurements. [Work supported by ONR Arctic Sciences Program.]
Comparison of experimentally observed long-range horizontal under-ice coherence in the Arctic with elastic scattering perturbation theory predictions.
Authors: Schmidt Henrik , LePage Kevin , Scheer Eddie
Published: October 2005

During the CEAREX ’89 experiment in the Arctic Ocean, long-range (≊200 km) coherent transmissions from an air gun positioned off the coast of Greenland were received on a horizontal array deployed from a drifting ice sheet located in the Fram Straits. These multichannel data have been analyzed for covariance on spatial scales of ≤1 km. Because in general the vectors connecting the receiver pairs are not parallel to the wave front vector of the propagating signal, these data contain information on both in-plane and out-of-plane scattering off the sea ice canopy. Assuming a modal (discrete) mean signal structure, the elastic scattering perturbation theory of Kuperman and Schmidt [J. Acoust. Soc. Am. 86, 1511–1522 (1989)] is used to estimate the structure of the scattered field. Comparisons are made between the observed coherence and that predicted by the theory for various isotropic or nonisotropic surface roughness power spectra, including power law spectra. [Work supported by ONR.]
The validity of the operator expansion method, a new formalism for wave scattering from rough surfaces.
Authors: Kaczkowski Peter J. , Thorsos Eric I.
Published: October 2005

A new method for computing wave scattering from rough surfaces has been proposed [D. M. Milder, J. Acoust. Soc. Am. 89, 529–541 (1991)]. The solution is obtained using a nonlocal operator that directly relates the surface values of the scattered field to the surface values of its normal derivative. This operator is expressed as a series of terms containing powers of an integral operator, which for a field incident on a flat surface provides the vertical derivative of the scattered field through Fourier transforms. The method has been applied to Dirichlet surfaces whose height varies randomly in only one direction (1-D surfaces) with either Gaussian or power law (Pierson–Moskowitz) spectra. Through comparison with an exact numerical method, the tapered plane-wave integral equation method [E. I. Thorsos, J. Acoust. Soc. Am. 83, 78–92 (1988)], the operator expansion (OE) solution is seen to have a remarkably broad region of validity, while its computational cost is orders of magnitude lower than that of the integral equation. Indeed, when computed to first order, the OE method is accurate when the Kirchhoff approximation is valid, and also when first-order small perturbation theory is valid, a result expected from the asymptotic properties of the analytical solution. Several numerical examples illustrating the wide accuracy of the rapid convergence of the OE solution will be presented. [Work supported by ONR.]
A novel approach to computation of aircraft noise contours.
Authors: Fidell Sanford , Reddingius Nicolaas , Smyth John , Sneddon Matthew
Published: October 2005

The software architecture of first-generation aircraft noise modeling software has historically limited its goals and necessitated adoption of numerous simplifying assumptions. Many of these restrictions may be traced to computational bandwidth restrictions in stand-alone computing environments. An ongoing independent research and development project has demonstrated the cost effectiveness of distributing acoustic detection calculations over networked workstations and other computers. A geo-information system approach to aircraft noise modeling has also been shown to support novel aircraft noise modeling capabilities, including single event predictions, observer-based contouring, consideration of terrain and other near-ground propagation effects, and perspective renderings and other manipulations of model outputs.
Temporal windows for signals presented at uncertain times.
Authors: Chang Paul , Viemeister Neal F.
Published: October 2005

A temporal analog of the Greenberg and Larkin [J. Acoust. Soc. Am. 44, 1513–1523 (1968)] frequency probe technique was used to measure the temporal window for detection of temporally uncertain signals. Percent correct responses for a 20-ms, 1-kHz signal presented in broadband noise was measured using a fixed-level 2IFC procedure. On 68% of the trials, the signal was synchronous with an LED flash and a contralateral click; on the remaining trials, the signal was presented asynchronously. Performance was best when signals were synchronous with the marker cues, and deteriorated monotonically as the interval between the signal and marker cues increased. The temporal windows measured in this way had durations of approximately 175 ms measured between the −3-dB points, more than a factor of 3 shorter than those obtained by Leis-Rossio and Small [J. Acoust. Soc. Am. Suppl. 1 80, S92 (1986)] using a similar technique. This indicates that the observer is not using the high degree of temporal resolution of which he is capable, and suggests a strategy whereby processing effort or attention is distributed over time. In a companion resolution experiment, subjects were able to detect intervals of the order of tens of milliseconds between the signal and the marker especially when the signal preceded the marker, providing further evidence that temporal processing is specific to the particular task or listening procedure that challenges the observer. [Work supported by NIDCD DC00683.]
Variational methods in acoustics: An assessment.
Authors: Pierce Allan D.
Published: October 2005

A predecessor of modern variational principles is Rayleigh’s stationary expression for the natural frequency, which is such that insertion of a ‘‘good guess’’ for the mode shape gives an ‘‘excellent’’ approximation for the frequency. It is now known how to construct principles such that the stationary expression corresponds to any physical magnitude of interest such as for example, the acoustic power radiated by a body in a given state of vibration. Application typically involves the exercise of some insight into the generic form of the trial functions, with a trade-off between simplicity and generality. Intermediate results tend to refine the insight and to determine what effects are of principal importance. Criticisms are that one usually has no firm knowledge of the accuracy and that the insight used in selection of the generic trial functions can be construed as subjective. The application often presents complicated multiple integrals with singular integrands, so it does not necessarily require less computational effort. The technique is, however, suitable for those with strong ‘‘physical’’ understanding of experimental and analytical results of analogous problems. For example, theoretical considerations predict specific singular behavior at corners and edges. Trial functions that incorporate such behavior will yield better approximations. From a broader viewpoint, variational principles can be used as a framework for the derivation of finite element idealizations, and from this viewpoint, there are no limitations on the achievable accuracy. Variational techniques should have an enduring role in the conceptualization of complex systems by simpler lumped-parameter and lumped-function models. One may legitimately question, however, whether they are needed for routine numerical predictions. [Work supported by the Office of Naval Research and by the William E. Leonhard endowment to Pennsylvania State University.]
Theoretical prediction of sound radiation from plates with holes.
Authors: Beslin Olivier , Millot Pascal , Guyader Jean-Louis
Published: October 2005

Sound radiation from plates with holes is of practical interest in the design of machinery hoods but is also of interest for double walls with one perforated panel. A theoretical model is established to calculate the pressure radiated in two rectangular rooms separated by a plate with or without holes. The acoustic field is built with a double layer potential integral equation, meaning that the plate introduces continuity of normal velocity and pressure jump on both sides of it [D. Ouellet, J. L. Guyader, and J. Nicolas, J. Acoust. Soc. Am. 89, 2131 (1991)]. The solution of the problem is derived using an expansion of the plate motion over a functional basis, and a two-dimensional expansion of the Green’s function of the room. Invacuo plate vibrations were presented previously [J. Acoust. Soc. Am. 89, 1868(A) (1991)] and conditions of convergence on natural frequencies and mode shapes were established. In the present paper, a short summary of these results is given, but it focuses on theoretical derivation of the vibroacoustic problem. The plate displacements and the pressure jump are calculated and then used to compute the pressure in the room. Numerical results on plate quadratic velocity and room quadratic pressure are presented, and convergence of the solution with the truncation of plate vibrations and acoustic pressure expansions will be established. Finally, the influence of holes on radiation is discussed. [Work supported by the Ministère de l’Environnement, S.R.E.T.I.E.]
A mixed BEM–FEM formulation for the numerical computation of the vibroacoustic behavior of vibrating structure.
Authors: Hamdi M. A.
Published: October 2005

A mixed variational formulation is presented as a powerful numerical tool for the analysis of the vibroacoustic behavior of complex structures like cars, airplanes, and spacecraft. It consists of coupling the displacement functional of the structure with a variational formulation by integral equations of both internal and external fluids. This method, which avoids singularities appearing in collocation techniques, takes into account absorbing materials and leads to an algebraic symmetric system of small size, which couples the acoustic loading on the fluid boundary to the acceleration of the vibrating structure. A powerful tool, based on an external coupling between Standard FEM softwares (ANSYS, ASKA, NASTRAN,..., etc.) with STRACO’s BEM software RAYON, is developed within the frame of EEC ESPRIT project (DYNAMO). As an industrial example this method has been applied with success. Numerical results are in good agreement with measurement obtained by Centre National des Etudes Spatiales (CNES) France, to the prediction of the vibroacoustic behavior of Ariane 4 launcher at take-off.
Higher-order discontinuous shape functions in boundary element codes.
Authors: Hahn Steven R.
Published: October 2005

Boundary element codes for acoustics use shape functions to approximate the pressure and normal velocity over the surface of individual elements. Many codes use zeroth order or constant interpolation over each element. A consequence of constant interpolation is that the surface quantities are discontinuous between elements. Higher-order shape functions have also been used and lead to models which converge more quickly than those using constant interpolation. Usually, the interpolation makes use of nodal points located along the edges of an element and results in the surface quantities being continuous. There are two limitations that result from this requirement of continuity. First, allowing the surface quantities to be discontinuous between elements often improves the accuracy of the nodal values. Second, modeling sharp corners can be difficult since the normal direction is not uniquely defined. This paper discusses the use of higher-order discontinuous shape functions where the collocation points are located on the interior of the element. Using several 2-D and 3-D examples, the accuracy and convergence of this technique is evaluated and shown to be superior to models using constant or continuous shape functions.
Cross-language word identification using durational cues only.
Authors: Mora Juan P. , de Jonge Catharina E. , Port Robert F.
Published: October 2005

Native and non-native speakers’ ability to identify highly similar words on the basis of durational cues was investigated. The phrases basket, boozedup, and buzzedit were obtained from five speakers pronouncing each phrase twice at three tempos. From measurements of segmental durations of the 90 tokens obtained, synthetic speech variants were constructed such that only durational information differentiated the three targets. Nine American and nine Spanish listeners identified the words in three conditions: grouped by tempo, grouped by rate, and ungrouped. Subjects heard a stimulus and chose the target phrase it corresponded to. Native speakers performed significantly better than non-native speakers, but both groups performed above chance. Grouping stimuli by rate or speaker did not much affect performance. Results suggest native listeners make better use of subtle durational differences between words that vary in speaker and rate than non-native listeners.
Auditory and visual perception of silent-center syllables.
Authors: Hura Susan L.
Published: October 2005

Silent-center syllables are defined as CVC syllables in which the vowel nucleus is attenuated to silence, leaving three or four pitch periods of consonant transition at either edge of the syllable. Previous studies [W. Strange, J. Acoust. Soc. Am. 85, 2135–2153 (1989)] have shown that subjects are able to identify vowels in silent-center (SC) syllables with nearly the same accuracy as for full syllables. These results have been used to support the theory of dynamic specification, where vowels are conceived of as gestures having intrinsic timing parameters. The current studies suggest alternate interpretations of the SC results. In the first study, the perception of a set of SC syllables was compared with that of full syllables at several signal-to-noise ratios. Contrary to previous experiments, it was found that identification performance was significantly better for full syllables than for SCs across signal-to-noise ratios. This suggests that, given a more demanding perceptual task, identification is hindered when the vowel nucleus is not physically present in the signal. The second study was a replication in the visual mode of earlier studies on SC syllables [W. Strange, J. Acoust. Soc. Am. 85, 2135–2153 (1989)]. Here, spectrographic analogs of full, SC, and other altered syllables were created. Subjects performed a matching task. Results were similar to those from the auditory domain, suggesting that more general perceptual processes may underlie the pattern of responses in both sensory modalities.
Progress in in
situ and vessel-mounted acoustic Doppler current profilers to measure zooplankton abundance.
Authors: Flagg Charles , Smith Sharon
Published: October 2005

Acoustic Doppler current profilers (ADCPs) offer a unique ability for studying biological structures in the ocean over a wide range of time and space scales. Studies of the capabilities of RD Instruments’ ADCPs operating at 307 and 150 kHz have been carried out to measure zooplankton abundance. A pilot study indicated that the method held great promise with an accuracy of about ±20% (Flagg and Smith, 1989). However, questions remained on the effects of differences in size class distribution and the use of ADCPs in noisier shipboard environments. Since then, long term insitu and shipboard ADCP results with simultaneous net data have been collected. The results show (1) that the ADCP’s ability to detect zooplankton density fluctuations to an accuracy of ±10% to 20% is confirmed, (2) that size class distribution fluctuations do not seem to have a major effect, and (3) that the quality and hence the range of the shipboard data is a strong function of ship speed and sea state. Dealing with shipboard data has proven difficult. Meaningful results are limited to regimes with very favorable signal-to-noise ratios.
An overview of noise control in the power industry.
Authors: Brooks Bennett M. , Brittain Frank H.
Published: October 2005

The owners and operators of power facilities are being increasingly confronted with problems of noise control. These problems are often lumped together with others under the umbrella of ‘‘Environmental/Health Issues’’ without recognition of their unique character. Properly addressed, these factors can lead to solutions that are well integrated into a plant’s design and operation. This overview presents the aspects of noise control that are both common with other industries and unique to the power business. Aspects unique to the power industry derive from regulatory and licensing requirements. Particularly for the community, it is demanded that the facility be ‘‘operable’’ in compliance with applicable noise limits. If regulations are not clear, successful operation may be determined by public acceptance. This is most often driven by the tonal content of the noise. Noise sources found in the power industry, such as fossil fired steam and combustion turbines, are discussed.
Cogeneration noise sources and control.
Authors: Bruce Robert D. , Bommer Arno S.
Published: October 2005

Gas turbines, heat recovery steam generators, steam turbines, air-cooled condensers, cooling towers, ventilation fans, and fuel-gas compressors all contribute to the noise environment associated with cogeneration plants. Both in-plant noise levels and community noise levels are of interest to the owner and the designer. The different methods for determining the sound power levels for these sources will be reviewed briefly and typical data for these sources will be presented. Gas turbines are usually housed inside special enclosures. In addition, the gas turbine enclosures and the steam turbines can be housed inside a building. Typical values of noise reduction will be reviewed for these constructions. In addition, other types of noise control treatments will be presented for each of the different sources.
Experiments on the active control of inlet fan noise from a JT15D engine.
Authors: Thomas R. H. , Burdisso R. A. , Fuller C. R. , O’Brien W. F.
Published: October 2005

A JT15D Pratt & Whitney engine is mounted in a test cell and operated at near idle conditions producing a fan blade passage frequency (BPF) of 2200 Hz. Flow disturbing rods are placed upstream of the fan to excite to dominance selective acoustic modes. A feedforward filtered-X adaptive LMS algorithm is implemented into a TMS320C30 DSP board. This controller is used to attenuate the BPF component of the fan noise. The BPF signal is sensed with a proximity probe placed in the plane of the inlet fan and provides the reference signal to the controller. This signal is input into an adaptive finite impulse response (FIR) filter whose output is fed forward into an array of 24 acoustic drivers attached to a ring mounted to the engine. The far-field acoustic error information is obtained from a microphone placed directly in front of the engine. The control algorithm then adjusts the phase and magnitude of the control signal to minimize the mean-square value of the error signal. Experiments have demonstrated reduction of the BPF noise component of up to 20 dB. [Work supported by NASA Langley Research Center.]
Measurements of nonlinear effects in the sound field radiated from a circular piston in water.
Authors: TenCate James A.
Published: October 2005

Computer-controlled positioning apparatus and a high-speed digitizer were used to make careful measurements of the nonlinear sound field radiated from a circular piston in water. Beam patterns of the fundamental and first several higher harmonics of a 1-MHz, 12-mm radius piston were measured. All the fine details in the beam patterns−including the additional sidelobes called fingers−are clearly evident. The measurements are compared with results from a computer code that solves the KZK equation for axisymmetric sources [see, e.g., Naze Tjo/tta etal., J. Acoust. Soc. Am. 88, 2859–2870 (1990)]. The agreement between experiment and theory/computation is remarkable. A measurement was also made of the attenuation with distance of a finger and the nearest sidelobe of the second harmonic generated from a 2.2-MHz, 3-mm radius piston. Measurements confirm the theoretical prediction that in the far field the finger and the sidelobe attenuate at different rates. [Work supported by ONR, David and Lucile Packard Foundation, Texas Advanced Research Program, and NSF.]
Ultrasonic four-wave mixing mediated by a suspension of polymer microspheres in water.
Authors: Simpson Harry J. , Marston Philip L.
Published: October 2005

An interaction analogous to optical four-wave mixing in photorefractive materials is demonstrated for ultrasonic waves in a suspension of spheres in water. Counterpropagating 800-kHz acoustical waves establish a standing wave field in ∼5% saline solution in which the suspended ∼20-μm-diam Latex spheres are neutrally buoyant. When these pump waves are absent, the spheres are distributed uniformly. In response to the imposed acoustical radiation pressure from the pump waves, the spheres are attracted to pressure nodes and form bands. An ultrasonic probe wave is incident on these bands in the form of a higher frequency tone burst. The banded suspension acts as a diffraction grating for the probe wave giving rise to coherent scattering from the suspension when the Bragg condition is satisfied. The Bragg scattering amplitude was studied as a function of the pump amplitude and compared to simple models. The scattered wave has the same frequency as the probe wave. The temporal evolution of the Bragg scattering amplitude in response to sudden changes in the pump amplitude was also studied. [Work supported by ONR.]
The use of focused shock waves to produce repetitive, high-speed water jets.
Authors: Mortimer Bruce J. P. , Jongens Adrian W. D.
Published: October 2005

The feasibility of using a focused shock wave in a water-filled elliptical cavity to produce repetitive, high-speed water jets with enough energy to eject small particles in a material sorting system was studied. A weak shock wave was produced by means of an electrical discharge at the one focus of the ellipse. The wave was concentrated under a nozzle located above the second focus where the high pressure caused a slug of water to be ejected out of the nozzle at high velocity. Electrical and mechanical factors influencing the jet performance were analyzed together with the results of a finite difference simulation of shock wave propagation in the elliptical cavity. High-speed photography was used to reveal the flight of the ejected water slugs.
Observations of screech of jets emerging from the 90° corner between plane reflectors, pertinent to valve noise.
Authors: Powell Alan , Kozu T.
Published: October 2005

The screech frequency of the free choked jet (nozzle 17.8×3.7 mm) was systematically lower (≊16%) than expected; first cell length and jet instability convection speed were even lower (≊23%, 30%). The sound intensity rose rapidly until pressure ratio R=3.0 (vice 2.3 expected), then more slowly; the jet spread angle (included) increased from 17° at R=2.2, to 35° at 3.0, then decreased to 20° at R=4.6. Pairs of reflectors (hard or soft) influenced the frequency negligibly, although cell length and convection speed changed. The intensity hardly changed (hard) yet the spread angle increased to 50° max (hard), or decreased, 22° max (soft). A third reflector, parallel to one and abutting the other, did not change the frequency but increased the intensity by 3–5 dB, increasing the spread angle only for R≳4. In all cases, a downward frequency jump occurred at R=2.16: the new mode is symmetric. [Work supported by Texas Advanced Research Program and Hitachi Ltd., Japan.]
Simultaneous masked thresholds as a function of masker bandwidth for different signal delays.
Authors: Wright Beverly A.
Published: October 2005

The improvement in signal detectability as signal onset is delayed relative to masker onset was measured as a function of masker bandwidth for notched and unnotched maskers. The signal was a 250-Hz-wide noise band centered at 2500 Hz. In two conditions, the 20-ms signal was gated 1 ms or 250 ms after the onset of a 420-ms masker. Signal thresholds were higher in the short-delay than in the long-delay condition. This difference generally increased as masker bandwidth increased and was similar in magnitude across the two masker types. Further, this difference was greatest for maskers whose spectra were symmetric about the signal frequency, and was smaller, and similar, for maskers that extended exclusively above or below the signal frequency. In a third condition, the signal was gated 1 ms after the onset of a 23-ms masker. Thresholds were highest in this condition, and varied differently as a function of masker bandwidth than in the other two conditions, particularly for the notched maskers. [Work supported by NIDCD award to Dennis McFadden.]
Detecting a tone of one frequency when a tone of a different frequency is amplitude modulated.
Authors: Yost William A.
Published: October 2005

It is assumed in many of the recent studies of cross-frequency effects of temporal processing that the effects are not occurring within any one frequency channel. This study was an attempt to investigate that assumption. A 500-ms carrier (the masker tone) of one frequency (e.g., 4000 Hz) was sinusoidally amplitude modulated at a slow rate (4, 8, or 16 Hz) and listeners were asked to detect a brief (10 ms) tone (the probe tone) presented at another frequency (e.g., 1000 Hz) and at different times relative to the phase of the masker modulator. Masker level was 75 dB SPL. If probe threshold varies as a function of the probe’s temporal relation to the phase of the masker modulator, then masker modulation might be preserved in the frequency channel of the probe indicating a within-channel interaction between the masker and the probe. There was a small (3–5 dB) variation of probe threshold when the probe was presented at different times relative to the phase of the masker modulator when the masker was modulated at 4 Hz and with 100% modulation depth. A similar change in threshold occurred when the masker was either higher or lower in frequency than the probe (mask is 4000 Hz, probe is 1000 Hz or mask is 1000 Hz, probe is 4000 Hz). No threshold changes were obtained at the higher modulation rates or at 4-Hz modulation when the depth of modulation was less than 100%. Thus there might be a small within-channel interaction, but only when the modulation rate is slow (i.e., 4 Hz). [Work supported by grants from the NIDCD and the AFOSR.]
Estimating unresolved roughness from echo amplitude fluctuations.
Authors: Stanton Timothy K. , Chu Dezhang , Mayer Larry , Courtney Robert
Published: October 2005

While bathymetric sonars use time of arrival measurements to map roughness features of the seafloor that are resolved by the sonar, they are unable to provide direct information regarding the relief that is within the sonar ‘‘footprint.’’ This relief is of interest to geologists interested in the morphology of the seafloor as well as acousticians who wish to predict sound scattering from both the resolved and unresolved roughness. In this talk, development and applications of a technique published by Stanton [T. K. Stanton, J. Acoust. Soc. Am. 75, 809–818 (1984)] in which the unresolved roughness of the seafloor is inferred from the degree to which the echo amplitude fluctuates from ping to ping as the sonar is towed over the bottom are presented. The shape of the Ricean echo amplitude PDF is related to applied to a set of broadband acoustic data collected in the Emerald Basin and compared with stereophotograph and core data. [Work supported by ONR.]