bluuebunny/crossref_metadata_2025 huggingface dataset:
Community annoyance by aircraft noise
Authors: Fields James M.
Published: October 2005

Rigorously designed social surveys, not public complaint actions, provide the most direct available evidence about the impact of environmental noise on residents. The balance of the available social survey evidence indicates that while personal attitudes affect noise annoyance, demographic characteristics and ambient noise levels do not affect annoyance with audible sounds. A continuously graded annoyance reaction to noise does not provide a strong scientific basis for choosing ‘‘highly annoyed’’ rather than any other degree of annoyance as an acceptability criterion. A rigorous synthesis of annoyance survey results must screen out erroneous data, use objective methods for selecting data sets, systematically adjust for important differences in nominal noise measurement conditions, weight data points by their precision, have a firm empirical basis for relating diverse annoyance measures, and satisfactorily evaluate the likely precision of the resulting synthesis curve. A theoretically sound justification for the form of a dichotomous dose/response curve must include a theory about the distribution of measured reactions to noise. Existing dose/response curves continue to make useful contributions to noise policy. Additional work will be needed before a synthesis of community dose/response relationships can be developed that meets the previously mentioned criteria.
New language and processes for examining environmental noise
Authors: Miller Nicholas P.
Published: October 2005

Guidelines and standards have been developed that identify the relationship between noise levels and land uses. These relationships were intended to define what land uses were ‘‘compatible’’ with specific levels of noise, but, in doing so, took into consideration not only public health and welfare, but also such concerns as the rights of property owners, available technology, and feasibility. The inclusion of these basically economic concerns meant that the noise and land-use compatibility guidelines would not necessarily protect people from all the adverse effects of noise or, perhaps more important, even identify when and where adverse effects might occur. This distinction between land-use compatibility and averse effects on people has generally been lost or overlooked. It is time to make this distinction clear. Case histories where pursuing land-use compatibility did not protect people from the adverse effects of noise or identify these adverse effects are discussed. A language and approach are proposed for clearly differentiating between the concepts of land-use compatibility and identification of disruptive effects.
Suggestions for solutions
Authors: Eldred Kenneth McK.
Published: October 2005

Solutions to some of the problems that inhibit effective functioning of the environmental impact evaluation process are suggested, including approaches for the use of metrics to improve communication with the affected public so that quantitative descriptions of both single-event and cumulative noise are more nearly related to the perceptions; development of guidelines for the definition of project study areas to include all who are anticipated to experience significant changes, quantification of individual changes in noise, as well as the net populations exposed to various levels, that address concerns within the entire study area; and research to improve our understanding of noise annoyance and its alleviation and to extend our noise modeling capability to areas further from airports then presently possible.
Error analysis of ocean acoustic tomography due to internal waves
Authors: Gozani J. , Boden L.
Published: October 2005

A realistic error analysis of the temperature variability of the oceans as probed by ocean acoustic tomography is presented. Travel-time errors resulting from fluctuating internal and surface waves are important in the analysis of the averaged time delays, which may indicate global warming trends due to the greenhouse effect. The 3-D propagation models through random media are extremely complicated. Propagation of model equations is governed by a set of matrix differential equations, whose elements are obtained by multidimensional oscillatory integration. Analytical and numerical studies have been conducted that show the feasibility of computing the matrix elements 1000 times faster than was previously done. The matrix equation is solved by well-known ordinary differential equation methods. The effects of frequency, trajectory, sound-speed profile, bathymetry, and the variances of internal and surface waves will be discussed.
Sound velocity in the deep sea: Examination of measurement data obtained from a deep submergence vehicle
Authors: Tsuchiya Toshio , Amitani Yasutaka , Ochi Hiroshi , Kikuchi Toshiaki
Published: October 2005

An accurate equation of sound velocity in seawater is a very important factor for ocean acoustic tomography according to acoustic travel time across the ocean. A sound velocity equation has been examined in a laboratory under various values of temperature, salinity, and pressure by Wilson, DelGrosso, Chen, and Millero. However, as direct measurement in the deep-sea area is very difficult, these data have been very limited. Therefore, recently the sound velocity was measured directly more than 50 times from the surface to a depth of over 6000 m by a sing-around sound velocimeter installed in the manned deep-sea research submergence vehicle ‘‘SHINKAI 6500’’ of the Japan Marine Science and Technology Center. Data were obtained with temperature, salinity, and pressure values in the western Pacific Ocean area. Then, the measured data were compared with the calculated values of the equation of Wilson, DelGrosso, Chen, and Millero. The comparison result indicated a trend: Sound velocity in the deep sea is greater than values of various equations according to the pressure effect.
Ultrasonic detection of icing onset and accretion thickness on aircraft
Authors: Hsu David K. , Margetan Frank J. , Wormley Samuel J. , Simpson Jeffrey A.
Published: October 2005

A major environmental hazard in aviation is ice buildup on aircraft. The development of a detector for the onset of icing and for accretion thickness measurement using ultrasonic waves is described. The detection is based on reflectivity change at a metal–ice interface and based on echo-ranging techniques using pulses of longitudinal and shear waves. The detector is sensitive to the onset of icing; ice layers as thin as 0.002 in. can be detected and accurate thickness can be measured from 0.015 in. onward. By using the ratio of an interface echo and an echo from an internal reference reflector, the quantitative measurement results are immune to changes in transducer coupling conditions. Using a combination of longitudinal and shear waves, the detector can also differentiate between ice and water. Laboratory tests were made for anticipated complications, such as rough or tilted surface of ice buildup and accretion of glaze versus rime ice. [Work supported by an Army SBIR grant to J-Tec Associates, Inc.]
Artificial conversational speech signal generation method for measuring characteristics of devices operated by speech signals
Authors: Nagabuchi Hiromi , Satoh Kanako , Kitawaki Nobuhiko
Published: October 2005

A method for generating an artificial conversational speech signal as the input test signal in measuring the characteristics of devices operated by speech signals, such as speech detectors, voice switches, and echo controllers is proposed. A state transition model among talkspurt, pause, double-talk, and mutual silence in conversational speech signals was introduced to simulate the statistical characteristics of these states in real conversational speech signals. This model assumed that the cumulative distribution of the duration time in each state is exponential. During talkspurt intervals, an artificial voice was generated using a speech synthesizer that controlled the spectrum and source characteristics independently. This artificial signal generation method can generate a signal with given characteristics by changing the values of system parameters, such as the average duration time of each state, transition probability from one state to another, and LPC (linear predictive coding) parameters that express short-term spectrum variation. The effectiveness of this artificial signal was demonstrated when used to measure the characteristics of a speech detector.
A speech separation algorithm that is robust to reverberation
Authors: Denbigh Philip N. , Luo Hongyue
Published: October 2005

An algorithm has been developed that can segregate overlapping voices by exploiting harmonicity. It is primarily a monaural method that relies on tracking pitch during the voiced parts of speech, and it does this successfully in spite of the spectral modifications imposed by room reverberation. The incoming waveform is divided up into frames that undergo spectral analysis by means of the FFT. Pitch determination is based on the subharmonic summation method, but tracking constraints are imposed that improve performance. First, the continuity of pitch is exploited by limiting the search for harmonics to the regions corresponding to the harmonics of the previous pitch measurement. Second, a condition is imposed whereby the amplitude of the harmonics cannot change significantly between frames. The combination results in a ‘‘two-dimensional harmonic sieve’’ that segregates voiced sounds. A remaining problem is that of associating a separated voice with the correct speaker when tracking is lost, for example, after a gap in voicing or after the pitch frequencies cross. For this, a binaural cue is invoked that relies on the average difference of arrival time of the relevant harmonics of one voice between two microphones. This also proves to be robust to reverberation.
Effects of ‘‘realistic’’ geoacoustic parameters on frequency-dependent bottom loss
Authors: Stoll Robert D.
Published: October 2005

Recent field studies have shown that seismic velocity and attenuation gradients vary rapidly in the sediments immediately below the seafloor. These variations have an important effect on the frequency-dependent bottom loss that is predicted for waves entering the bottom at low grazing angles for several reasons. The more obvious reason is the variable path length traversed by the shallow diving waves that are returned to the water column; however, a second important reason appears to be the conversion of some p-wave energy to s waves resulting from the weak coupling between the two wave types that is caused by the high-velocity gradients near the bottom. Comparisons of bottom loss computed using the conventional constant gradient models and variable-gradient models based on recent field measurements show significant differences in bottom loss as a function of frequency. The additional effects of p- to s-wave conversion are also illustrated. [Work supported by ONR, Code 11250A.]
Seismoacoustic beamforming with a linear array of geophones on the seafloor
Authors: TenCate J. A. , Muir T. G. , Shooter J. A. , Manning J. F. , Kristensen Å. , Caiti A. , Michelozzi E.
Published: October 2005

Experiments were carried out in the Straits of Sicily, Malta Channel where the seafloor is a relatively flat silty sediment some 150 m deep. A linear array of ten vertically gimballed geophones with element separations of 5 m was laid out on the seafloor. Measurements were made on seismic fields created by explosive shots. Similar experiments were performed in Vestfiord, Norway, where the seafloor is mud over glacial till. The seismic waves of primary interest at these sites are the dispersive Scholte waves. Group velocity dispersion curves from several different shots were derived using the multiple-filter method and show both sites to be isotropic. From these curves the phase velocity as a function of frequency was obtained. A beamforming algorithm was implemented that accounted for the change in seismic velocity with frequency. This enabled the array to be beamsteered on the shot signals providing array responses at various frequencies. The resulting directivities and sidelobe characteristics were in good qualitative agreement with array theory. Since seismic velocities were quite low (50–130 m/s), narrow beams were formed at low frequencies; half-power widths at 18° at 7 Hz to 13° at 11 Hz were obtained with an array only 50 m in length. [Work supported by Defense Advanced Research Projects Agency, Maritime Systems Technology Office.]
Influence of geoacoustic modeling on predictability of low-frequency propagation in range-dependent, shallow-water environments
Authors: Cederberg R. J. , Siegmann W. L. , Jacobson M. J. , Carey W. M.
Published: October 2005

In a previous study of predictability of relative intensity and horizontal wave numbers by the authors, parabolic approximations were used in range-independent shallow-water waveguides. Uncertainties in sediment properties were found to be the most significant factor limiting prediction accuracy. In this paper, models of bottom sound-speed profiles that take into account sediment consolidation are developed, and their effects on propagation model predictions in range-dependent environments are examined. Environmental parameters correspond to those near the site of a recent New Jersey Shelf experiment site. Using borehole density data and Biot–Stoll theory, a functional form for porosity in a homogeneous consolidated sediment is derived. Corresponding sound-speed profiles for different sediment types are then constructed. Predictions from models consisting of consolidated sediment layers throughout the bottom are compared with results from cases for which sound-speed is comprised of piecewise linear segments. In addition, bottom sound-speed range dependence was modeled with discrete as well as continuous changes between profiles for variations of the geophysical parameters in this area and no substantial difference was observed. Comparison of experimental data with model predictions incorporating range dependence are discussed. [Work supported by ONR.]
Simple 3-D Gaussian beam calculations for a standard and a modified wedge
Authors: Bucker Homer
Published: October 2005

In many practical Navy acoustic systems, the sound field is strongly affected by three-dimensional variations in the ocean bottom. A theory is presented for a simple Gaussian beam propagation model that accounts for full three-dimensional effects of the ocean bottom. The Gaussian beam formulation is especially useful because it defines the sound field in terms of the travel times and angles of eigenrays that are needed for the analysis of acoustic systems. Examples will be shown for the standard wedge calculation [Deane and Buckingham, J. Acoust. Soc. Am. 93, 1319–1328 (1993)] and for a wedge modified by an island and a knoll.
Long-range continuous-wave and time-domain simulations of ocean acoustic scatter from a subbottom anelastic corner
Authors: Chin-Bing Stanley A. , Murphy Joseph E. , Li Gongqin
Published: October 2005

Recent long-range acoustic reconnaissance experiments done in the mid-Atlantic ridge region show strong reverberation from many ocean bottom features. Two types of features characteristic of this region, and possible contributors to this reverberation, are seafloor ridge corners—‘‘inner’’ corners and ‘‘outer’’ corners—formed by two ridge faces intersecting at near-right angles. Corners formed by faces intersecting at near 90° are termed ‘‘inner’’ corners and those formed by faces intersecting at near 270° are termed ‘‘outer’’ corners. Via computer simulations, the effects of an anelastic seafloor corner on the acoustic field originating from a distant source have been investigated. Both an ‘‘inner’’ corner and an ‘‘outer’’ corner were used in the study. The effects of thin sediment layers covering the corners were also investigated. Simulations were made using continuous-wave (cw) computer models: the parabolic equation model, fepe, for long-range propagation of the acoustic fields to and from the vicinity of the corners, and the seismoacoustic finite-element model, safe, to determine the scattered fields from the anelastic corners. Time-domain calculations were obtained from FFTs of the cw fields. Examples will be presented that show the effects from these two corner types. [Work supported by NRL, ONR, and the ONR Acoustic Reverberation SRP.]
Resonance scattering from nonspherical bubbles in water
Authors: Feuillade C. , Werby M. F.
Published: October 2005

Submerged bubbles can be treated as air-filled inclusions in water from which scattering occurs because of the change of acoustical impedance at the interface between the two media. The T-matrix expansion technique allows for the general description of scattering from both spherically and nonspherically shaped bubbles. This method is used to study the monopole acoustical resonances of bubbles deformed into elongated axisymmetric objects (specifically, prolate spheroids and cylinders with hemispherical endcaps). The results confirm that the resonance frequency of a bubble increases when it is deformed from a spherical shape, but show that it is also independent of the direction of excitation and increases more quickly with aspect ratio for cylindrical than for prolate spheroidal bubbles. The frequency width of the resonance increases with the deformation in both cases, but Q falls more quickly for the cylindrical bubble. Increasing the deformation causes the scattering amplitude to decrease and its angular distribution to change. A remarkable result is that for highly deformed spheroidal bubbles there is relatively little change from the spherical scattering pattern obtained with an undeformed bubble. In contrast, highly deformed cylindrical bubbles show prominent lobes. [Work supported by ONR Technology Directorate (Element 602435N) and by the Naval Research Laboratory, 6.1 Program (Element 601153N). Technical management provided by NRL–SSC.]
Angular dependence of acoustic backscatter from simulated anisotropic Goff–Jordan seafloor relief
Authors: Premus V. , Alexandrou D.
Published: October 2005

The angular dependence of 12-kHz acoustic backscatter from simulated anisotropic centimeter-scale bottom relief is investigated for angles of incidence between 0° and 20°. Numerical simulations of backscattering strength as a function of elevation and azimuth are obtained by merging the Kirchhoff approximation with realizations of seafloor topography derived from the Goff–Jordan surface model. The surface model has been theoretically extrapolated to the small-scale roughness regime by connecting the spatial sampling interval with the incident acoustic wavelength and defining the characteristic wave numbers, kn and ks, of the 2-D surface roughness spectrum to be O(m−1). The viability of extending the Goff–Jordan model to centimeter-scale relief is supported by the recent observation of power-law spectra within the spatial frequency range of 0.01 to 1.0 cycles/cm [D. R. Jackson and K. B. Briggs, J. Acoust. Soc. Am. 92, 962–977 (1992)]. The results demonstrate that backscattering strength can be very sensitive to azimuthal variation in surface correlation properties. It is also observed that the spectral roll-off parameter has an important impact on the minimum degree of anisotropy that can be identified by the backscattered acoustic signature. [Work supported by ONR through Contract No. N00014-93-I-0049.]
High-resolution backscatter from the Mid-Atlantic Ridge
Authors: Makris Nicholas C. , Berkson Jonathan M. , Menis Richard
Published: October 2005

High-resolution backscatter is charted to respective scattering sites on the western flank of the Mid-Atlantic Ridge (MAR) by two-way travel-time analysis and beamforming. Since the range resolution of the low-frequency FM acoustic data is on the order of the acoustic wavelength (roughly 6 m), a bistatic mapping procedure is employed that accounts for bathymetric variation and combines calculations of eigenray paths and slant range to precisely locate scattering sites at ranges up to roughly one-half a convergence zone from the source/receiver. Right–left ambiguity of the horizontal-line-array data is resolved by taking advantage of the environmental symmetry-breaking properties of transmission loss, modeled with the parabolic equation, as well as by inversion of adjacent quasimonostatic observations. Mapped reverberation and estimated scattering strength are then projected onto high-resolution bathymetry for comparison. For the same scattering site and observation geometry, it is found that higher-resolution signals often yield higher and more localized scattering strength maxima. This suggests that discrete and spatially intermittent scatterers are important to reverberation in the MAR.
Use of explicit duration models in speech recognition
Authors: Fong Cynthia , Ostendorf Mari
Published: October 2005

Although researchers have observed that automatic speech recognition errors are often associated with improbable duration patterns, current recognition systems take little advantage of known durational cues. In addition to using simplistic models of duration, recognizers put very little weight on durational probabilities (because of the high dimensionality of the feature vectors typically used). This work explores the benefits that can be gained in speaker-independent continuous speech recognition from more accurate duration modeling and automatically estimating a duration score weight. In the context of the stochastic segment model, segment durations are modeled using gamma distributions conditioned on phonetic, lexical, and phrasal context, as well as speaking rate. Robust parameter estimation, a potential problem with the large number of different conditioning factors, is achieved using automatic clustering techniques with a maximum likelihood criterion. A by-product of the clustering procedure is a better understanding of the relative importance of the conditioning factors. Speech recognition experiments on the resource management task show that simple context-independent gamma distributions give similar results to nonparametric relative frequency models, and that error can be reduced by more than 10% by conditioning models on such factors as prepausal position, speaking rate, and lexical stress.
A corpus-based model of interstress timing and structure
Authors: Bachenko Joan , Gale William A.
Published: October 2005

Studies of interstress intervals tend to be more suggestive than conclusive because they rely on relatively few speech samples. The study reported here is based on observations taken from 32 000 intervals in the read speech of 106 speakers. A phone recognizer was used to label the onset times of each phone; intervals were identified as the span between stressed vowel onsets and each interval was classed according to its structure (the number of consonants and reduced vowels it contained) as well as duration. The data showed strong regularities in the dependence of time on classification. A model mixing duration, interval structure, and prior probabilities was then constructed and tested on phone lattices; the lattices were generated by the phone recognizer for speech from the resource management task. When durations were fixed but interval structure varied, prior probabilities pruned incorrect answers significantly better than chance; the mixed model’s improvement was inconclusive. However, when both durations and interval structure were varied, the mixed model was clearly superior. The results indicate that interval duration and structure might be a link between speech and grammar in human and machine speech recognition.
High-resolution and efficient multiple-string hypothesization using interword models
Authors: Chou Wu , Matsuoka Tatsuo , Juang Biing-Hwang , Lee Chin-Hui
Published: October 2005

A new accurate string hypothesization algorithm to find multiple-string hypotheses for speech recognition is proposed. The algorithm differs from the conventional N-best search algorithms in that it allows the use of the same long-term language (bigram) models and the same set of subword models, including the interword models, to perform both forward tree search and backward tree-trellis stack decoding. The proposed A*-based backward tree-trellis stack decoding can handle interword units at the word boundaries, including the word boundaries of one-phone words. Therefore, the interword context dependency is exactly preserved in both forward and backward multiple-string hypotheses search. The search efficiency is maximized by applying the same high-resolution acoustic and language models in both search directions. When the search heuristics are used, the proposed approach provides a more accurate string model matching than that of the conventional time-synchronous beam search decoder. The proposed algorithm was tested on 24 000 connected digit strings recorded over the telephone network and collected from ten regions across the United States. Using a set of interword subword unit models, the test results showed that 62.4% string errors can be corrected if the second-best string hypothesis can be used to replace the wrong strings. The string error rate was decreased from 2.75% (657) to 1.0% (247) using the top two string hypotheses.
Comparison of WG11 study variability to that of other interlaboratory studies
Authors: Nixon Charles W.
Published: October 2005

The variability of the data measured in the WG11 interlaboratory study was compared with that measured in three other interlaboratory studies conducted in this country, in Europe, and in the Scandinavian nations. All studies utilized a real-ear attenuation at the threshold measurement paradigm and basically followed the procedures described in the current ANSI and ISO hearing protector measurement standards, with one major exception. The WG11 study utilized naive subjects and hearing protector fitting procedures that were relatively free from experimenter influences instead of the trained subjects and the ‘‘best fit’’ procedures required by current measurement standards. A subject fit (only hearing protector manufacturer’s printed instructions handed to the naive subjects) and an informed user fit (manufacturer’s instructions plus experimenter general comments to the naive subjects only relative to the instructions) were utilized for the WG11 study measurements. Comparisons indicate that the variability of the data collected under the less rigorous subject and fitting procedures of the WG11 study is at least equivalent to that measured in the other interlaboratory studies.
A discussion of WG11’s anthropometric data with comparison to other available databases
Authors: Ohlin Doug
Published: October 2005

Anthropometric and demographic data were complied from four participating laboratories on subjects used in WG11’s round-robin testing. Age and sex distributions were compared to sizing distributions of the single-flange (V-51R) and EP-100 earplugs. Earplug size was generally found to increase with age, while females were found to be skewed toward the smaller sizes and males toward the larger sizes. Measurements of ear length, ear breadth, pinna protusion, and head height were compared to military standards for anthropometric data.
Absorption of finite-amplitude ultrasound in biomedical tissue
Authors: Li Ping-Wah , Blackstock David T.
Published: October 2005

A theoretical investigation of the absorption of finite-amplitude ultrasound in biomedical tissue is reported. The tissue is modeled as a medium having multiple relaxation processes. A generalized Burgers equation, which includes the effects of nonlinearity and relaxation, is derived. Analytical and numerical solutions of this equation for a step shock, a periodic wave, and a temporal Gaussian pulse are presented. The results are used to calculate the finite-amplitude absorption coefficient and temperature rise in the tissue. It is found that nonlinear distortion causes the absorption and the temperature rise to be significantly higher than that for small-signal ultrasound. [Work supported by NIH, ONR, and ARL:UT IR&D.]
High-frequency (10–25-MHz) wave propagation in argon at pressures up to 10 MPa
Authors: Chiang C-H. , Bond L. J.
Published: October 2005

Acoustic wave propagation in gaseous argon has been investigated using a high-power ultrasonic gated-tone-burst transmission system. Results of measurements of compression wave absorption and velocity in argon at frequencies 10 to 25 MHz, at static pressures up to 10 MPa, at temperatures of 21 to 23 °C, and at high power (above critical intensity 16.97 W/m2 at 10 MHz and 10 MPa) are presented. For small-amplitude waves at pressures up to 2 MPa, the resulting data are in good agreement with that predicted using ideal gas equations and fundamental thermophysical gas constants. At static pressures higher than 4 MPa and for higher-power settings, distortion of the waveform is observed. Excess attenuation, in addition to classical absorption, is also found at higher power settings. With a 10-MHz fundamental frequency, significant second harmonic generation is observed. The data are compared with existing theories for finite-amplitude waves in fluids. Current theories [F. Dunn etal., IEEE Ultrason. Symp., 527–532 (1981); A. L. Thuras etal., J. Acoust. Soc. Am. 6, 173–180 (1935)] for harmonic generation and attenuation are shown not to predict the observed experimental data for high-power, high-frequency waves in argon at high pressure.
Detection and generation of transient acoustic microcavitation at 4.3-MHz center frequency
Authors: Xu Qihong , Zheng Xiaoyu , Apfel Robert E.
Published: October 2005

To study the potential bioeffects caused by applications of medical diagnostic ultrasound, a highly focused transducer with center frequency at 4.3 MHz was used to generate microcavitation in water seeded with polystyrene particles, and the cavitation was detected by a modified active detection system [R. A. Roy etal., J. Acoust. Soc. Am. 87, 2451–2458 (1990)]. The results show that the cavitation threshold is about 4.0 MPa in water seeded with polystyrene particles of 0.1 μm diameter. The mechanical index corresponding to the cavitation threshold is 2.0, which is in the upper range of diagnostic ultrasound. The results also show that the cavitation depends strongly on the size of the polystyrene particles added in the water. [Work supported by NIH through Grant No. R01 CA39374.]
An electrical-discharge, steam-bubble acoustic source—theory and experiment
Authors: Olson Allen H. , Sutton Stephen P.
Published: October 2005

Electrical energy stored in a high-voltage capacitor bank is rapidly discharged into seawater. Smooth spherical electrodes are used to achieve nearly uniform heating of the seawater in the inner-electrode gap. This allows the water to be superheated, in the liquid state, without electrical breakdown. As the high-pressure, high-temperature liquid expands against the surrounding hydrostatic load, the phase transition to steam occurs. The rapid volume growth of the steam bubble then gives rise to a very broadband, high-frequency acoustic pulse. Experimental data are presented for 1.9-cm-diam electrodes separated by 1.0 cm in 20 Ω cm seawater. The electrical resistance is shown to be a function of the energy delivered to the water. A fully three-dimensional conduction model is presented that takes the electrode geometry and known physical properties of seawater as input. The computation proceeds in constant energy steps, with spatial variation in temperature, electrical conductivity, and electric potential updated at the end of each step. The model accurately predicts the observed electrical resistance and the onset of steam formation.
Standard viscoelastic material
Authors: Wetton R. E. , Duncan J. C. , Foster G. M.
Published: October 2005

Whereas the moduli of elastic solids and the viscosities of simple molecular liquids are well-defined, such that many can be used as standards, the same is not true of viscoelastic materials. The properties of the latter are by definition both frequency and temperature dependent. In this paper some candidate materials and the results obtained over a wide (−100 to +100 °C) temperature range and a fairly wide measurement frequency range (0.01–100 Hz) are considered. In order to extend this frequency range, particularly into the kHz range, the time–temperature superposition ideas of Williams, Landel, and Ferry are used. This necessitates the material conforming to this treatment by virtue of possessing a temperature-independent relaxation spectrum, to a good approximation. In order to have relatively high damping at ambient, the polymer has to have a Tg around 0 °C, and, to be thermorheologically simple, it has to be predominantly single phase. The best candidate materials have been found to be random copolymers of butadiene and acrylonitrile.
Efficiency of viscoelastic materials in the vibration reduction of thin rectangular plates
Authors: Lapointe R. , Cheng L.
Published: October 2005

The problem of reducing structural vibration with viscoelastic materials while adding the least extra weight possible has always been of great interest, especially in the aeronautic field. To study this, the system consisting of a thin rectangular plate covered by (unconstrained) sections of viscoelastic material that are also rectangular will be used. The minimization of the vibration level of the plate when subject to external forces using a determined weight of coverage will then be treated, with special attention given to the frequency- and temperature-dependent characteristics of the viscoelastic materials. The mathematical model of the system is first developed following the Love–Kirchoff plate theory and a polynomial Rayleigh–Ritz approximation. The search for the minimal level, using the simulated annealing technique, is then initiated. Numerical results will be presented and opportunities for using these results for more complex systems will be discussed.
Development of a new hearing protector test standard—Overview of the efforts of ANSI S12/WG11
Authors: Berger Elliott H.
Published: October 2005

In 1987, ANSI S12/WG11 (previously designated S12-26) was given an expanded scope and a new title, namely, FieldEffectivenessandPhysicalCharacteristicsofHearingProtectors. The WG was directed to explore the problems inherent in using optimum-performance laboratory-derived real-ear attenuation data to estimate achievable and/or typical workplace protection, and to identify or develop procedures that could yield improved estimates of field performance. After careful deliberation, the WG determined that a new laboratory-based real-ear attenuation at threshold procedure with explicitly defined subject selection, training supervision, and fitting techniques could potentially provide useful estimates of obtainable field performance. The WG devised a draft protocol and subjected it to a pilot study [Berger etal., J. Acoust. Soc. Am. Suppl. 1 88, S10 (1990)]. Subsequently, the protocol was modified and utilized in a full-scale test of three types of earplugs and one earmuff, by four independent laboratories. The testing was conducted from September 1990 through December 1991. This presentation begins with an overview of the hearing protection rating problem and the rationale for the activities of WG11, as well as an introduction to the remaining invited papers in the session, which focus on the needs for improved hearing protector attenuation data and the results of the interlaboratory study.
Modeling and analysis of low-angle ice canopy reverberation in the Arctic
Authors: Duckworth Greg , Farrell Ted , LePage Kevin , Atkinson Cola
Published: October 2005

Recent advances in modeling coherent loss in the Arctic have made it possible to attempt a constrained inversion of monostatic Arctic reverberation for the ice scattering matrix. An analysis is presented of low-frequency active reverberation data collected in the Central Arctic in 1992 where such an inversion yields meaningful results and compare them to theoretical predictions. Historical and measured ice roughness statistics collected in tandem with the acoustic portion of the experiment were used to obtain elastic perturbation theory predictions of scattering loss and backscatter. These losses were integrated into the Kraken normal mode model to yield highly accurate predictions of the coherent signal structure to very long ranges in the Arctic waveguide, as verified by TL measurements. Based on these predictions, a significant portion of the time/frequency structure of the backscattered return received on a 256-element hydrophone array was modeled. To construct a well-conditioned inverse problem, propagation in 10-Hz bands was divided into three distinct groups; surface duct, mid depth and RSR. Modeling of TL and travel time for each band/group made it possible to invert the energy in the backscattered return for the average scattering cross section of the ice cover at the three discrete group grazing angles. Comparison of the derived scattering strengths with the elastic perturbation theory predictions yielded good agreement. [Work supported by ONR.]
Experimental investigation of features of low-frequency broadband acoustical signal propagation in shallow water
Authors: Petnikov V. G. , Kozelsky A. R. , Lynch James F.
Published: October 2005

In shallow water, the combination of downward refracting sound-speed profiles and strong sound absorption by the bottom limits the range of (tomographic) transmissions and causes one to use lower-frequency broadband signals. In this paper, investigations of low-frequency broadband (25–95 Hz) acoustic signal propagation in a slightly variable shallow waveguide with a negative water column sound-speed gradient are presented. An experiment was carried out in the Barents Sea along a 14-km stationary track. In travel time tomography in shallow water, as in deep water, the resolvability and identifiability of the acoustic arrivals is a necessary condition. In this experiment, seven stable arrival peaks are noted. Over 2 hr, these peaks fluctuate in rms travel time by several milliseconds, which is consistent with the measurement accuracy of the system used. Identification of the arrivals using both mode theory and rays with beam displacement, combined with the ambiguity diagram approach of Munk and Wunsch, has shown that some of the arrivals are resolvable modes and some are resolvable rays.
Materials for thermoacoustic generation of sound
Authors: Ward William C. , Gabrielson Thomas B.
Published: October 2005

Thermoacoustic generation of sound underwater represents a technology distinctly different from conventional underwater transduction. By proper design, there is potential for high-power, low-frequency generation of continuous-wave, pulsed, or modulated output. From a materials point of view, there are three major components: the stack, which maintains the temperature gradient responsible for pumping the acoustic oscillations; the working medium, which supports the internal acoustic oscillations; and the heat exchangers, which supply energy from an external source to the stack. Each of these subsystems has critical thermal and acoustical requirements that constrain the selection of materials and the overall source configuration. Thermal conductivity, viscosity, and specific heat replace piezoelectric constants and stress-strain relationships as fundamental properties. In addition, the acoustic performance is modeled more effectively as a waveguide than as a lumped-parameter system. Many of the advantages and disadvantages of this source technology are readily apparent in the context of materials selection and configuration. [Work supported by the Naval Space and Warfare Systems Command, PMW-183.]
Hot topics in psychological acoustics
Authors: Yost William A.
Published: October 2005

Psychological acoustics, or psychoacoustics, is the study of the relation between sound and the behavior of humans and other animals. Such relations are usually referred to as ‘‘hearing.’’ In recent years, the psychoacoustical study of hearing has returned to a major question, ‘‘How does an organism determine the sources of sound in its environment, especially when there are a number of simultaneously presented sound sources?’’ The sensory receptors for hearing are sensitive to the physical properties of the sound field impinging on the organism and are not selective for processing sound sources. The brain must process the neural code of the incoming sound field in order for the organism to determine the sources of the sound that make up the input sound field. The neural code for sound provided by the auditory peripheral nervous system is a temporal–spectral representation of the total sound field. This talk will highlight recent developments in simulating the temporal–spectral code provided by the auditory periphery and advances in the study of properties of this code that might be used by the brain to aid the organism in determining the sources of sounds. [Work supported by NIDCD and AFOSR-Life Sciences.]
Low-frequency backscatter from near-surface bubble plumes
Authors: Schindall Jeffrey A. , Roy Ronald A. , Crum Lawrence A. , Carey William M.
Published: October 2005

Anomalous low-frequency backscatter from the sea surface is governed by a variety of near-surface effects. Principle among these are microbubble distributions and their subsequent effects on the local sound speed structure. Although a rigorous explanation of these scattering results (including the presence of spikey events often observed in both deep water scattering experiments and sonar trials) would likely require consideration of a host of physical acoustic mechanisms, Occum’s razor would dictate that a simple explanation can be both effective and illuminating. This paper examines the role of monopole radiators, the simplest form of radiation, beneath a rough pressure-release surface to explain the presence of low-frequency false targets. It is shown that for certain sea state conditions such false targets can result from transient bubble plumes acting as acoustically compact scatterers. An attempt will also be made to estimate, from the combined probabilities of the presence of white caps and the likelihood that a given bubble plume possesses the requisite volume fraction to produce such an event, the number of false targets to be expected as a function of sea state. [Work supported by ONR and ARPA.]
Quantitative backscattering coefficients from the numerical scattering chamber
Authors: Stephen R. A. , Swift S. A.
Published: October 2005

Models of geoacoustic interaction with the seafloor are essential to link the backscattered acoustic field with geological and geophysical descriptions of the seafloor. Beamforming has been implemented into numerical scattering chamber formulation so that backscatter coefficients and functions can be obtained. This process is discussed for a flat, homogeneous seafloor; a single facet on a flat, homogeneous seafloor; and a canonically rough, homogeneous seafloor. This study suggests that representing the backscattered field by a single, angle-dependent coefficient is an oversimplification. Coherence of the scattered field across the beam before stacking and the time spread of the stacked field are significant issues. The numerical stacking chamber computes solutions to the elastic (or anelastic) wave equation by the finite difference method in a two-dimensional Cartesian geometry. The finite difference approach has the following advantages: (a) it includes all shear wave (rigidity) effects in the bottom; (b) it can be applied to pulse beams at low grazing angles; (c) both forward-scatter and backscatter are included; (d) multiple interactions between scatterers are included; (e) arbitrary, range-dependent topography and volume heterogeneity can be treated simultaneously; (f) problems are scaled to wavelengths and periods; and (g) the method considers scattering from structures with length scales on the order of acoustic wavelengths.
A null field T-matrix perturbation formalism for scattering from a fluid–elastic interface with random surface roughness
Authors: Bishop Garner C.
Published: October 2005

A null field perturbation formalism for scattering a pressure wave from a fluid–elastic interface with random surface roughness is developed. Helmholtz–Kirchhoff integral equations and the elastic tensor boundary conditions are used to represent the unknown scattered and surface pressure and displacement fields. The null field hypothesis is used to obtain a system of coupled integral equations for the surface fields. Perturbative representations of the scattered and surface fields and of the matrix elements of the Helmholtz–Kirchhoff integral equations are constructed and used to develop equations for the nth-order spectral amplitudes of the unknown fields. It is shown that the nth-order spectral amplitude of a scattered field is coupled to the nth-order spectral amplitudes of all scattered fields and to all lower-order spectral amplitudes of all surface fields. Consequently, the nth-order T-matrix may be calculated recursively and expressed in terms of the zeroth-order off-shell T-matrix elements. The T matrix for the nth-order spectral amplitude of the scattered pressure field in the fluid is calculated, and it is shown that scattering process is mediated by excitation of all possible intermediate surface states created by mode conversion of all lower-order surface field states.
Dynamic mechanical properties of S2WG79 viscoelastic polymer samples and other composite materials
Authors: Collier Robert D.
Published: October 2005

S2WG79 candidate materials for standardization have been measured in accordance with procedures recommended by the Working Group. The measurements have been performed with the Tufts viscoanalyzer with a frequency range up to 1 kHz. Results for the candidate materials include complex Young’s modulus, shear elastic modulus, and associated loss factors as a function of frequency and temperature. Multi-sample testing provides statistical measures of measurement errors and sample variations. Results are presented in formats for ready comparison with those of other investigators. In addition, results of research on cured epoxy resins and selected dental composites illustrate relationships between measured glass transition temperatures and composite material compositions.
Determination of the static moduli of viscoelastic polymers
Authors: Reader Wayne T. , Sauter David F.
Published: October 2005

The characterization of viscoelastic polymers frequently requires determination of the static moduli in addition to determination of the dynamic moduli. A commonly applied method for determining the static Young’s or shear modulus is to extrapolate the dynamic modulus in the rubbery regime to vanishing low frequency. A second approach is to relate the hardness, e.g., Shore A, to an estimate of the Young’s or shear modulus. As will be briefly described, neither of these approaches appears to provide consistent results. A method is described that exploits the stress/strain hysteresis loop to develop estimates of the static moduli. The method is believed to provide more reliable estimates than obtainable from the previously employed methods. Examples are provided of the method’s application to a variety of viscoelastic polymers possessing loss factors varying from about 0.1–1.0, and rubbery moduli varying from 1–10 Mpa. Comparisons are made between the results of the new method and the two previously used ones. [Work supported by ONR 1225AM.]