bluuebunny/crossref_metadata_2025 huggingface dataset:
Sound speeds and absorptions in a sandy sediment
Authors: Sabatier James M. , Lawrenson Christopher C. , Shadwick James B. , Hickey Craig J. , Shields F. Douglas
Published: October 2005

A sediment tank 11 ft deep and 10 ft in diameter has been installed at the National Center for Physical Acoustics. This tank has been instrumented with a vertical array of B&K 8103 hydrophones along the axis of the tank, and has been filled with washed ‘‘pit run’’ sand. In studying the sound transmission through the sediment, the hydrophones are used both as senders and receivers. The tank is being used to develop ‘‘shaded’’ array transducers for sub-bottom profiling for measuring sound speeds and absorptions in sediments. Difficulties have been experienced in getting a homogeneous sediment. However, two distinct waves have been observed. The first is a fast wave with a velocity equal to approximately 1600 m/s that propagates readily at frequencies up to 100 kHz. The second is a much slower wave that cuts off above 2 kHz and has a velocity of a few hundred meters per second. Experiments are under way to determine the frequency dependence off the speed and absorption of these two waves. Calculations are being made in an effort to explain theoretically the experimental results. [Work supported by ONR, MMRI.]
Nonlinear acoustic scattering from trapped gas bubbles in sandy sediments
Authors: Boyle Frank A. , Chotiros Nicholas P.
Published: October 2005

A nonlinear backscattering model for trapped bubbles in sandy sediments was developed. A difference frequency scattering coefficient is computed via a technique similar to that of Ostrovsky and Sutin [NonlinearSoundScatteringfromSubsurfaceBubbleLayers, NaturalPhysicalSourcesofUnderwaterSound, edited by B. R. Kerman, pp. 363–373 (1993)], which treats the case of bubbles surrounded by water. The Biot theory is incorporated to model the acoustics of a sandy sediment. Biot fast and slow waves are included by modeling the pore fluid as a superposition of two acoustic fluids with effective densities that differ from the pore fluids’ actual density and account for its confinement within sediment pores. The principle of acoustic reciprocity is employed to develop an expression for the backscattering strength. [Work supported by ONR under management by APL/UW.]
The detection of objects buried in sand using airborne sound-induced seismic vibrations
Authors: Sabatier James M. , Troutman Tom M.
Published: October 2005

Objects buried in air-saturated sand can be detected by measuring the normal component of matrix velocity or acceleration in the vicinity of the object. A loudspeaker positioned 1.15 m away and 1.15 m above the surface is driven in the frequency range between 1 and 4.2 kHz. Geophones, accelerometers, and an off-the-shelf laser Doppler vibrometer are used to measure the normal velocity component. Surface images of the object are formed by making many point velocity or acceleration measurements with a geophone or accelerometer. An LDV will also be used to produce noncontact, scanned images of small targets in sand. The resolution of this technique is discussed. Also, water-saturated sand will be investigated.
Dynamic response of axisymmetric poroelastic cylindrical bone
Authors: Paul H. S. , Murali V. M.
Published: October 2005

The dynamic response of axisymmetric poroelastic bone subjected to transient pressure along the curved surface of the cylinder is studied. In the analysis, exact solutions that satisfy the boundary conditions are obtained by applying Laplace transformations to the equations of motion and fluid flow. The Laplace inversion is obtained from the residue theorem. The stress component σrr* (dimensionless) is plotted with T (dimensionless time) for various η* (dimensionless decaying parameter). It is seen that the stresses behave alike for different η*. In the region 1<T<1.5, for η*=2 a slight oscillation is present. The stress component σ* (dimensionless) is plotted for the same parameters. Similar behavior is exhibited with the crossing of curves for η*=2 and 3. The comparison between the elastic and poroelastic behavior of stress σrr* for η=1 is carried out. It is seen that there is rapid oscillation for the elastic case, while it is absent in the poroelastic case. For larger time there is no significant effect of stresses. It appears that the elastic constants of material which are considered without porosity may not exist in nature.
Acoustics in the first 100 years of The Physical Review
Authors: Beyer Robert T.
Published: October 2005

Recently, the American Physical Society published a volume entitled ‘‘The First One Hundred Years of the Physical Review,’’ containing 1200 pages of reprints of ‘‘seminal papers.’’ Unfortunately, there are no acoustics papers in that volume. This paper attempts to redress the balance by discussing a number of significant acoustics papers that have appeared in ThePhysicalReview, especially in the years before the appearance of TheJournaloftheAcousticSocietyofAmerica.
Calibrating the methods of stationary phase and steepest descent
Authors: Nagem Raymond J. , Collins Brian J.
Published: October 2005

Analytic modeling of radiation from sources or scattering by obstacles near submerged layered environments generally leads to Fourier-type spectral integrals with integrands that contain pole and branch point singularities. In the high-frequency range, there are spectral intervals in which the integrands are highly oscillatory, thereby making their numerical evaluation problematic, especially in the vicinity of singularities that lie on the Fourier path in the absence of dissipation. Various methods of performing the numerics are examined, including deformation of the real-axis integration path into a contour in the complex plane, on which the integrand has weak or no oscillations and is exponentially damped away from a local maximum. By comparing the corresponding steepest descent and stationary phase analytic approximations with the numerics, one may calibrate these algorithms for accuracy, especially when saddle (stationary) points and singularities are in close proximity. The physical wave phenomena associated with these alternative analytic models are discussed. Attention is given to the separation of the integrand into weakly and highly oscillatory portions, as required in the analytic approximations.
Acoustic field in a borehole within a layered formation
Authors: Wang Xiuming , Zhang Hailan , Ying Congfu
Published: October 2005

In acoustic well logging, the borehole may be considered as a vertical waveguide of infinite cross section with horizontal discontinuities, and the conventional mode expansion cannot be applied. Some authors introduced an artificial large coaxial cylindrical boundary, transforming the problem into one with finite cross section. However, this approach is limited to low frequency. Based on the theory of generalized function, the mixed spectrum of the infinite cross-section waveguide is analyzed and a new hybrid method is proposed in which the acoustic field is expressed as a sum of several discrete modes and an integral of continuous modes with unknown weight functions which are obtained by numerically solving a group of integral equations deduced from the boundary conditions at discontinuities. It is shown that this method makes it possible to calculate up to the frequency for a typical logging environment. Laboratory experiments have been conducted in which a specific method was adopted to form a liquid cylinder surrounded by fluid layers. Both studies reveal that the reflection of the guided wave at the discontinuity is strongly dependent on the wave frequency. When the frequency is low the reflection is prominent, but at a high frequency the reflection is much weaker.
Exploring the parameter space of low frequency of sonoluminescence
Authors: Jankovsky Joseph C. , Ketterling Jeffrey A. , Apfel Robert E.
Published: October 2005

An experimental apparatus has been designed to measure the physical properties of low-frequency sonoluminescence (SL) (15 kHz). Radial motion of the bubble has been measured by Mie scattering and also by a new method, which images the bubble through a magnifying CCD camera illuminated by a strobing LED lamp. The light emission of SL is measured by a photomultiplier tube. An automated gas handling system has been constructed in order to measure the effects of various gas mixtures and concentrations on SL. The system consists of voltage actuated valves, a mixing vessel, and pressure sensors, which are interfaced to a computer and controlled using the LabVIEW programming environment. With the lower frequencies and the resulting larger bubbles, it is hoped that the parameter space for this region of SL can be mapped out. [Work supported by NASA through JPL Contract No. 958722.]
A numerical investigation of the relative scattering of Biot fast and slow waves by a spherical inclusion in a poroelastic medium
Authors: Yelton Dennis J. , Stern Morris
Published: October 2005

The relative scattering of Biot fast and slow wave pulses by a spherical inclusion in a poroelastic medium is computed by applying the single frequency steady-state solution of Zimmerman and Stern [J. Acoust. Soc. Am. 94, 527–536 (1993)] to the discrete Fourier components of an incident pulse, and employing linear superposition. The solution of Zimmerman and Stern is an analytical series solution whose convergence is primarily determined by computation precision, which imposes certain limits on the frequency and size of the inclusion. Within these limits, the scattered signals are computed as a function of scattering angle and range for broadband incident fast and slow wave pulses. The findings are compared to experimental observations. [Work supported by the Naval Research Laboratory, Stennis Space Center.]
Application of a stochastic inversion method for estimating the sound speed in the ocean bottom
Authors: Ohta Kazuhiko , Morishita Itaru , Ozaki Shunji , Ishiwata Tsuneo
Published: October 2005

A stochastic inversion method is applied to the problem of determining sound-speed profile in bottom sediment from modal eigenvalues, which can be observed from the FFT beamformed output of a horizontal array in a range-independent shallow-water waveguide. Under a noisy field, each observed eigenvalue has different variance depending on the signal-to-noise ratio (SNR) of modal peaks in the output wave-number spectrum; this difference in SNR originates from the relation between mode shape and source/receiver depths. Thus by using those variances in a covariance matrix involved in stochastic inversion method, it is numerically demonstrated that we can improve the estimation for the solution as compared to that obtained by using a uniform covariance matrix. It is also shown that combination of the same modal eigenvalues observed at the different source or receiver depth can reduce the variance of estimated solution. Application of the stochastic inversion method to real data is also discussed together with comparison with a regularization method. [Work support by JDA.]
The history and development of the steelpan
Authors: O’Connor G. Allan
Published: October 2005

The history and development of the steelpan is a fascinating story, from its beginnings as a folk instrument in its native Trinidad to a musical instrument played thoughout the world today in calypso, popular, jazz, and classical music. Various steelpans will be demonstrated.
Acoustics of steelpans
Authors: Rossing Thomas D. , Hampton D. Scott , Hansen Uwe J.
Published: October 2005

Steelpans are characterized by strong coupling between note areas partly due to nonlinear vibrational effects. Experimental and theoretical studies of their vibrational behavior will be discussed, and the origin of the rich spectra of harmonic overtones explained in terms of this behavior.
Formant synthesis: Turning cascade into parallel with applications to the Klatt synthesizer
Authors: Lin Qiguang , Zou Jingyun
Published: October 2005

Formant speech synthesis is one of the successful approaches for text-to-speech synthesis. Usually, formants are connected in parallel for the synthesis of consonants and in either cascade or parallel for vowels. The cascade structure requires a fewer number of control parameters and the synthesized spectrum is guaranteed to be correct. It is best suited for vowel synthesis. However, because of the necessary interchange of a parallel and cascade structure, it is not trivial to maintain good continuity in resonance modes. On the other hand, vowels can also be synthesized by the same parallel formant synthesizer used for consonants. This solution avoids the interchange of resonators, but more control parameters are necessitated and the resultant spectrum may be distorted. In this paper, a method is described which mathematically turns a cascade configuration into parallel. No additional parameters, that is, the complex amplitudes of formants, are explicitly required. Instead, these parameters are determined from given formant frequencies, bandwidths, and the higher-pole correction. The method thus maintains continuity in resonance modes without requiring extra parameters. The method has been integrated into the Klatt synthesizer. Synthetic speech generated using the proposed method will be demonstrated. [Work partially supported by ARPA Contract No. DAST 63-93-C-0064.]
The effects of systematic duration changes on phonemic transformations
Authors: Chalikia Magdalene H. , Parvey Natasha
Published: October 2005

Previous studies show that listeners who are presented with a repeated sequence of steady state vowels (between 30–100 ms each) report hearing illusory changes in the identity of the speech sounds, a phenomenon called phonemic transformations [M. H. Chalikia and R. M. Warren, Lang. Speech 34, 109–143 (1991)]. The organizations are pretty salient and can be recognized at a later time. In previous studies all vowels were initially at the same duration. In this study, the vowels within a sequence had different durations (baseline stimuli), to resemble characteristics of real speech utterances. The effects of manipulating systematically the duration of individual vowels by increasing or decreasing the duration of each vowel relative to the baseline is investigated. Twenty-six subjects were asked to listen to the baseline stimuli and record what they heard with each. Then, they were asked to match each of the additional vowel sequences to the forms heard with the baseline ones. Matching performance decreased for the short durations (10–60 ms/vowel), but not for the longer ones (40–180 ms/vowel).
The use of surface wave dispersion for source ranging
Authors: Penshorn Jason T. , Smith Randall W.
Published: October 2005

Surface wave dispersion curves (velocity versus frequency curves) are used to estimate source range. The data used in this study consist of signals, due to an impulsive source, received on a line array of triaxial seismometers. The first step in the ranging method is the estimation of the surface wave dispersion curve. This is accomplished via the use of the continuous wavelet transform as a time-frequency decomposition. The known dispersion curve is then used in conjunction with the time-frequency decomposition of the received signal to estimate source range. The method and some preliminary results were presented previously [Smith etal., J. Acoust. Soc. Am. 97, 3310(A) (1995)]. This presentation focuses on the effects of receiver separation and signal-to-noise ratio on the ability to accurately estimate the surface wave dispersion curve, and the corresponding effects on the source range estimates.
Estimation of spatial backscatter power spectra from sonar images
Authors: Jaffe Jules S.
Published: October 2005

Two- and three-dimensional power spectral estimation from sonar backscatter images is an important area of research that has ramifications for understanding the underlying structure of many environmental features. In one case, that of backscatter from groups of animals, the interanimal correlation distances are the inverse Fourier transform of the three-dimensional power spectrum. Estimation of three-dimensional power spectra from sonar data is made difficult because of the spreading of the sonar beams as a function of range which results in a lower resolution image. In multidimensional signal processing parlance, the resulting collected sonar data have been convolved with a spatially variant kernel. Standard signal processing methods have difficulty when applied to these kinds of functions, as the usual assumption is that the data have been obtained from a spatially invariant kernel. A method is proposed to estimate the power spectrum of such images by first starting with an ensemble. It is shown how the spatially variant problem can then be converted into a spatially invariant problem. Straightforward methods for power spectral estimation are then used to determine the spectrum. Examples of the use of the methodology on three-dimensional sonar data will be used to illustrate the method.
An adaptive threshold target detection and estimation algorithm
Authors: Chandran Girish , Jaffe Jules S.
Published: October 2005

An algorithm to isolate multiple targets reflecting multiple correlated signals arriving at a receiver is described. The algorithm stems from a specific application, an active high-frequency, three-dimensional imaging system that is used to image zooplankton [Jaffe etal., ‘‘FTV: A Sonar for Tracking Macrozooplankton in 3-dimensions’’ (to appear in Deep Sea Research)]. The signals that are transmitted are designed to have flat cross-correlation properties. The receiver algorithm exploits this property of the transmitted signal set and works by iteratively isolating progressively weaker targets at each iteration step. An important feature of the structure is the ability to adapt the threshold of the detectors of different signals to targets of various strengths. The algorithm leads to a receiver structure which is a modification of the classical parallel matched filter bank to detect targets and estimate their parameters. Experiments were performed in a tank to test the receiver structure. Various objects were suspended in known configurations and then two signals were transmitted at them. The algorithm was successfully able to isolate the targets and estimate their positions and strengths. [Work supported by NSF Grant No. OCE 9421876.]
Acoustic imaging with radiation imaging operators
Authors: Raza Mohammed I. , DuBroff Richard E. , Herrick Thomas J.
Published: October 2005

A differential operator has been formulated, which can be used to remotely detect boundaries and position of objects from remote data. The operator has been called the radiation imaging operator (RIO). The RIO is composed of local characteristic parameters and local derivatives of the acoustic wave. After operating on the wave distribution, the output gives a minimum at the boundary of the object, when the correct values of the characteristic parameters are used. The RIOs are developed from radiation boundary conditions (RBCs) and the relevant material boundary conditions (MBCs). The RBCs were formulated [B. Engquist and A. Majda, Math. Comput. 31, 629–651 (1977)] to simulate the propagation of out-going waves without any significant reflection at the truncating boundary. The MBCs are in the form of Dirichlet and Neumann boundary conditions. A finite-difference time-domain algorithm is implemented to image objects using the discretized RIO, where the shape and location of object is not known. The imaging technique has been found to be robust and tolerant to a reasonable amount of noise.
Spectrum space-time signal processing matched with an antenna’s motion, medium, and noises
Authors: Gorban Igor I.
Published: October 2005

There have been many works connected with working out and researching high-quality space-time signal processing (STSP) algorithms matched with medium and noises. However, there has been far less research into the question of STSP algorithms matched with the motion of the antenna in space, especially in the case of the three-dimensional motion of the antenna with variable velocity, angle rotations, and modified form. The aim of this paper is to present the results of research in the field of STSP matched with the complicated motion of the antenna, the medium, and the noises together. This research developed from the author’s earlier research that was presented at the conference on Computational Acoustics and its Environment Applications, Southampton, UK, 1995. In this paper the integral equations that describe maximum likelihood STSP matched with the complicated motion of the antenna, inhomogeneous medium, and additive Gaussian space-time correlated noises, have been obtained. Special ways for solving the equations were proposed and high-quality spectrum STSP algorithms were found for partially coherent and stochastic signals. The new and the former algorithms were compared in different conditions. It was found that in many cases the new algorithms were essentially better than the former ones.
Benchmark cases for range-dependent seismoacoustic propagation codes
Authors: Goh Joo Thiam , Schmidt Henrik
Published: October 2005

Benchmark solutions exist for range-dependent acoustic propagation in fluid-only media [J. Acoust. Soc. Am. 87, 1497–1545 (1990)]. However, not many reference solutions are available for the case of mixed fluid-elastic media. Some simple canonical benchmark problems are presented and the solutions from four different computational methods are compared. They are the elastic PE [J. Acoust. Soc. Am. 93, 1815–1825 (1993)], boundary element method [J. Acoust. Soc. Am. 89, 1629–1642 (1991)], wave-number integration approach [J. Acoust. Soc. Am. 97(A), 3316 (1995)], and a spectral superelement formulation [J. Acoust. Soc. Am. 98, 465–472 (1995)]. Both forward and backscattered results are presented. A common thread in the last three approaches is the use of the SAFARI/OASES code as a Green’s function generator. Conclusions regarding the general performances of these methods are drawn for the various test cases. [Work supported by ONR.]
Wave-based extraction of ocean bottom impedance from constant frequency transmission loss measurements
Authors: LePage Kevin D.
Published: October 2005

One method of characterizing the propagation in a shallow-water region is to collect a series of measurements which together form a composite of the range-dependent transmission loss (TL) between a source and receiver at single frequencies. Here, a wave-based method of extracting the bottom impedance matrix is presented. As opposed to traditional approaches to extracting environmental information from these measurements, where the bottom properties are perturbed until the modeled and the measured transmission loss agree, the wave-based method is a two-part method, where the horizontal wave numbers of the waveguide are first determined such that all the features in the measured TL are accounted for, and then the water column properties are used in conjunction with a finite-difference scheme [M. B. Porter and E. L. Reis, J. Acoust. Soc. Am. 77, 1760–1767 (1985)] to determine the bottom impedance at these wave numbers. One attraction to this approach is that most features in the data are modeled, and all the unique information about the bottom is contained in an impedance matrix over horizontal grazing angle and frequency. Since many of the unknown physical processes which affect shallow-water transmission are concentrated in the bottom, modeling issues are reduced by this approach.
Short-range seismoacoustic propagation on and off the beach
Authors: Dorman LeRoy M. , Sauter Allan W. , Bradley Chris , Wiggins Sean , Porras Javier
Published: October 2005

Cultural seismic noise (noise caused by human activities) can be used for tracking and surveillance. During June and July 1995, a field experiment, dubbed ‘‘Adaptive Beach Monitoring’’ was conducted on both sides of the shoreline at U.S. Marine Corps Base Camp Pendleton, near Oceanside, California. Various sources were observed by seafloor seismic and acoustic sensors (four ocean-bottom seismometers), and by a 24-element seismometer array ashore. Preliminary results on the propagation of surface (and interface) waves shows that the surficial shear velocity is similar on both sides of the shoreline (nominally 250 m/s). The dispersion of the waves is, however, markedly different. The dispersion of Scholte waves observed on the OBSs was strong, with group velocity varying by a factor of 2 in the 2- to 10-Hz range. Ashore, however, Rayleigh waves in the 5- to 20-Hz frequency range showed little or no dispersion. [Work sponsored by the Office of Naval Research, Code 32.]
Applications of optimized rational approximations to parabolic equation modeling
Authors: Cederberg R. J. , Collins Michael D. , Siegmann William L.
Published: October 2005

Rational approximations designed using least-squares constraints are easy to obtain and have useful applications. The coefficients are defined in terms of accuracy constraints on the propagating part of the spectrum and stability constraints on the rest of the spectrum. Among the applications are a filtering operator as well as improved approximations for the split-step Padé solution [J. Acoust. Soc. Am. 93, 1736–1742 (1993)] and radiation boundary conditions for outgoing wave equations [Clayton and Engquist, Geophysics 45, 895–904 (1980)]. An efficient operator filter is obtained by designing a rational approximation that is the identity function (or a weighted function) over the propagating (or desired) spectrum and decays to zero elsewhere. Operator approximations have previously been applied to replace the operator in the interior of the domain (the parabolic wave equation), generate radiation boundary conditions, solve scattering problems, and generate initial conditions. With the improved approximations, it is possible to use range steps of more than a hundred wavelengths with the split-step Padé solution. By enforcing both accuracy and stability constraints, it should be possible to overcome stability problems [Howell and Trefethen, Geophysics 53, 593–603 (1988)] and obtain useful higher-order radiation boundary conditions for outgoing wave equations.
Geoacoustic profile estimation by inversion of head wave data
Authors: Chapman N. Ross , Hannay David E.
Published: October 2005

An approach is described for estimation of geoacoustic model parameters in shallow water based on inversion of head wave data obtained in experiments with vertical line arrays (VLA). Analysis of head waves obtained in seismic refraction surveys with horizontal arrays is a widespread practice in exploration seismology. However, in shallow water, there can be practical advantages in the use of VLAs. Inversion of head wave data obtained with a VLA provides estimates of the layer depths, and compressional wave speeds and attenuations. Three inversion techniques are compared: inversion of travel time versus range data for a single sensor, direct measurement of the critical angle using the VLA, and inversion of travel time versus hydrophone depth data for a specific range. The techniques are applied to data from an experiment on the continental shelf off Vancouver Island. Shallow explosive charges were used as sound sources out to ranges of 5 km. Strong head wave signals were recorded from two distinct layers, and the data were inverted using the travel time versus depth method. The estimated values of 1750 and 1900 m/s for the compressional wave speeds are consistent with results from conventional seismic surveys in the vicinity.
Bathymetrically refracted modal eigenrays and bottom attenuation: A paradoxical relation
Authors: McDonald B. Edward
Published: October 2005

Shallow ocean acoustic propagation generally results in bathymetric refraction toward deeper water, and is accompanied by bottom attenuation. In modal eigenray calculations involving small horizontal grazing angle interactions with bathymetry, cases have been found [Heaney etal., J. Acoust. Soc. Am. 90, 2586–2594 (1991)] in which path integrated bottom loss actually decreases with increasing mode number. This apparent paradox is resolved by showing that the increase in modal ray turning rate with mode number can exceed the accompanying increase in bottom attenuation rate. Thus fixed angular deflection can imply attenuation which decreases with mode number. Investigation of acoustic eigenmodes leads to an algebraic relation between bathymetrically induced rates of horizontal ray turning and modal energy loss. This relation gives the modal attenuation rate per increment of horizontal ray turning, and is expressed in dB per radian. The dB per radian relation is in general not a monotonic function of mode number. Implications of this result may be relevant to observations in the Heard Island Feasability Test. [Work supported by NRL and Scripps Institute of Oceanography.]
Acoustic properties of marine sediments in the North West Shelf of Australia
Authors: Thomson P. Philip , Dunlop John I.
Published: October 2005

Mathematical models for characterizing the propagation of acoustic waves in shallow water require knowledge of such acoustic properties as dilatational velocity, attenuation constant, shear velocity, and attenuation of the seafloor. Insitu measurement of these properties is difficult due to the remoteness of the sea bottom. There are uncertainties in predicting these properties from geological features such as porosity, grain size, density, etc., and there is a need for direct measurements. This paper outlines some exploratory work on the laboratory measurement of core samples taken from the North West Shelf of Australia and subsequent mathematical modeling to predict general propagation characteristics. The sound-speed ratio and attenuation constant were measured by timing a high-frequency wave packet through a length of sediment core. Shear wave measurements were made using a similar measurement frame with piezoceramic bender disk transducers of 1- to 2-kHz resonance frequency. Before making measurements, the samples were individually evacuated in a mild vacuum for a short period and then slowly infused with seawater at room temperature. Measurements were made at three different positions in the cores corresponding to different depths.
The long/short vowel distinction in Māori—A preliminary study
Authors: Sullivan Kirk P. H.
Published: October 2005

In Māori, vowels are considered to be intrinsically either long or short. Orthographically a long vowel is marked with a macron. The distinction in vowel length is used contrastively and results in word pairs such as mātau (to know) and matau (right, as in not left). There are inconsistencies with length marking even internally within Māori language dictionaries [e.g., Williams, ADictionaryoftheMaoriLanguage (GP, 1971)]. The long vowels have previously been considered sequences of two identical short vowels [Krupa, MorphemeandWordinMaori (Mouton, 1966)]. The question of what phonetically distinguishes a short vowel from a long vowel and whether these can be distinguished from two consecutive examples of the same short vowel at a morpheme boundary, for example, arises. The current preliminary study aims to examine the durational range of long and short vowels and to determine the factors to be investigated in a longer study. The results relate to one male speaker. Whether a vowel was long or short was marked in the orthographic version of the data by a single speaker. The results are discussed in relation to the factors to be investigated in further studies.
Variability of vowel formant frequencies and speaker normalization: The cases of Mandarin and Taiwanese
Authors: Huang Kuo-You , Tseng Chin-Hsing
Published: October 2005

Formant frequencies of vowels produced by male and female speakers of Mandarin and Taiwanese were measured. Twenty Mandarin-Taiwanese bilingual subjects produced three tokens of each vowel in the /lV/ (for Mandarin) and /kV/ (for Taiwanese) contexts. Like previous studies with other languages, women’s formants were higher than men’s in frequency, that high vowels had F1 values lower than low vowels, and that front vowels had F2 values higher than back vowels. Bark-difference measures were obtained from the Bark-transformed formant frequencies; that is F0 was subtracted from F1, F1 from F2, F2 from F3, F2 from F4, and F3 from F4. Two Bark-difference measures (i.e., F1−F0, F3−F2) correspond well to vowel height and point of articulation, respectively. Most importantly, high vowels have F1−F0 values within 3.5 Bark and front vowels have F3−F2 differences also within 3.5 Bark. These transformations largely reduced the between-speaker variability related to the gender factor. Results of these Mandarin and Taiwanese vowel data agree with English data [A. K. Syrdal and H. S. Gopal, J. Acoust. Soc. Am. 79, 1086–1100 (1986)] and support the universality of the category-independent auditory theory of normalization.
Local algorithms for controlling an active piston damping system
Authors: Arabadzhi Vladimir V.
Published: October 2005

A scattering and/or emitting surface with local (of small wave dimensions) piston emitters located directly on it is considered. The problem of active sound damping by the quantity of prior information on the wave field and surface properties are classified. It is shown that in some practically significant cases one may do without traditional accumulation in a damping system of the entire information ‘‘imprint’’ of the wave field. The aim of the paper is the construction of the most local algorithms. Four control algorithms are described in the paper: (a) the algorithm of the maximum of the total average for the period of the absorbed power on the pistons, (b) the algorithm of the iterative compensating of the sound pressure on pistons, (c) the algorithm of the compensating of the volume velocity, (d) the algorithm of the physical surface in accordance with the incident wave. The results of the action of algorithms (a)–(d) is the transformation of the distribution of normal oscillating velocities on a given surface to the region of high (weakly emitting) space frequencies. A joint solution of the problems of radiating and scattering damping is achieved too.
Parametric silencer
Authors: Arabadzhi Vladimir V.
Published: October 2005

Total dimensions of the silencer of exhaust gas noise usually are in finite relations with the sound wavelength, corresponding to the engine assigned frequency. A silencer design independent of assigned frequency is suggested. An ultrasound sirenlike flux cyclical switch ensures the N-cascade up-conversion of the pulsing frequency into the ultrasound frequency range, where the small-dimensional sound absorbers may be used. N cascades ensure low-frequency pulsing amplitude decreasing by 2N times. The output cascade tube diameter must be more than the input tube diameter by √2 times to save the average in time total flux cross section. This circumstance is the main factor that limits a decrease in the size of the silencer dimensions. The results of experimental investigations of the one-cascade system are presented.
A simplified model of a thermoacoustic refrigerator
Authors: Prosperetti Andrea , Yuan He
Published: October 2005

The simplified approach to thermoacoustic prime movers described at earlier ASA meetings is extended to the case of heat pumps. The mathematical model is described and a weakly nonlinear theory is developed. The impact of the gas pressure, stack geometry, resonator shape, and other design parameters is explored. [Work supported by the Office of Naval Research.]
Shipboard electronics thermoacoustic cooler
Authors: McKelvey D. , Ballaster S. , Garrett S.
Published: October 2005

A thermoacoustic refrigerator that was optimized for preservation of biological samples in space, was modified for use as a cooler for the CV-2095 shipboard radar electronics rack. The thermoacoustic cooler was tested in the laboratory and demonstrated at sea aboard USS DEYO (DD-989). In the laboratory, using a calibrated heat load, the data acquisition system was able to account for the total energy balance to within 4%. At the highest operating power aboard ship, 227 W of acoustic power was used to provide 419 W of useful cooling power, corresponding to a coefficient of performance of 1.85. Taking into account the 54% electroacoustic efficiency of the loudspeakers, the shipboard electronics thermoacoustic cooler (SETAC) provided 1 W of cooling for each watt of electrical power input. [Work supported the Office of Naval Research and the Navy Science Assistance Program.]
Holographic interferometry: An approach to study the unsteady temperature fields in the stack region and its neighborhood
Authors: Herman C. , Wetzel M. , Wagner J.
Published: October 2005

Holographic interferometry combined with high-speed cinematography is a measurement technique, which allows the investigation of unsteady temperature distributions without affecting the physical process. Therefore it is the most suitable measurement technique for the investigation of the oscillating temperature field in the stack region and its neighborhood. In order to apply holographic interferometry, vibrations of the experimental setup have to be kept below a fraction of the wavelength of the used laser light, 514 nm. The first research efforts were focused in the design and verification of a feasible experimental setup which satisfies the requirement of low vibrations. Currently, temperature measurements, applying holographic interferometry to our thermoacoustic refrigerator model, are carried out. From the obtained interferometric fringe patterns the temperature distribution can be reconstructed quantitatively applying digital image processing. Results of these measurements will yield valuable information about the heat transfer mechanism occurring in the stack region and its neighborhood, which can be used to improve the heat exchanger design. [Work supported by the Office of Naval Research; Martin Wetzel is also supported by a scholarship from DAAD.]
Statistical measures of transfer functions in complex structures
Authors: DeJong Richard G.
Published: October 2005

The frequency response function of structures can be modeled with pole-zero functions or as modal summations. Either representation can be used to obtain probability distributions for the magnitude of the frequency response functions. These probabiltiy functions range from trigonometric functions for simple structures to log-normal distributions for complex structures. Examples are given for simulated and measured frequency response functions of beams, plates, and vehicle structures. The statistical measures obtained from frequency averages are similar to those obtained from ensemble averages in complex structures. This suggests that a sufficiently complex structure can be considered ergodic in the frequency domain.
Active sound extraction for noise control in the presence of duct mean flow
Authors: Madanshetty Sameer I. , Chu Boa-Teh
Published: October 2005

A method of controlling noise level in duct flows is described. The method is based on the principle of energy extraction by active source(s), rather than by wave cancellation as in ‘‘antisound.’’ As such, the method of energy extraction is robust; it does not need the delicate signal processing, perfect phase, and amplitude matching, crucial to sound cancellation. An improved control strategy useful for both low and high frequencies is described, and its effectiveness in the presence of mean flow is analyzed. It is found that in the presence of through flow the control is effective in extracting energy from any waves traversing it. As the duct flow Mach number increases the control appears to be less effctive for waves produced upstream of it but it is more effective for the waves produced downstream of the device. Further, this conclusion remains valid whether the detector is placed on the upstream or downstream side of the control device.
Primary and secondary sound transfer functions in an active noise control earplug
Authors: Olree Keith T. , Harley Thomas R.
Published: October 2005

Active noise control in a headset or earplug typically attempts to lower the sound level at an error microphone located close to the ear. If the transmission path between the error microphone and the eardrum for the primary noise is different to the path for the secondary noise, a reduction at the error microphone may not lead to a reduction at the eardrum. In fact, if these paths are sufficiently different a reduction at the error microphone may actually lead to amplification at the eardrum. An example of a possible cause for differing transmission paths is the bone conduction effect that becomes noticeable in occluded ear canals. In this study, a probe microphone was inserted into the ear canal of human subjects. This microphone was used to measure the pressure near the eardrum for primary and secondary sound sources. The pressure was also measured at an error microphone of an active noise control earplug. These measurements will be presented and some of the implications for active noise control will be given.
Experimental results using active control of energy density
Authors: Sommerfeldt Scott D. , Parkins John W. , Park Young C. , Rhea Zane M.
Published: October 2005

Previous research reported has presented numerical results obtained, indicating that one can often achieve improved global control of an enclosed acoustic field by minimizing the acoustic energy density, rather than the acoustic pressure. Inexpensive sensor probes have been developed that are capable of sensing the pressure and velocity components of the acoustic field, for incorporation into an adaptive control system that minimizes the energy density. The control system has been implemented within an enclosed sound field and has been used to compare the global attenuation achieved by minimizing either the squared pressure or the energy density. The control system is capable of implementing control with multiple sources and/or sensors. Results are shown for the low modal density case in the enclosure and indicate the improved global attenuation that can be achieved using energy density control. As well, the dependence of the controlled field on error sensor location is shown to be substantially weaker when controlling energy density than when controlling squared pressure. [Work supported by NASA Langley Research Center.]
Acoustic indices of production mechanisms underlying tonal ‘‘grunt’’ calls in baboons
Authors: Owren Michael J. , Seyfarth Robert M. , Cheney Dorothy L.
Published: October 2005

Free-ranging baboons (Papiocynocephalusursinus) produce brief, tonal ‘‘grunt’’ calls in a variety of social circumstances. These calls bear a striking resemblance to human vowels, being composed of regular, apparently harmonic energy forming several prominent energy peaks below 5 kHz. This resemblance was tested by examining 216 grunt calls from nine adult female baboons for clues to the mechanisms apparently involved in their production. Comparisons of spacing of purported harmonics in grunt frequency spectra to the results of other pitch-extraction methods strongly supported the supposition that these calls are produced using regular vocal fold vibration at approximately the same rates found in adult humans. Examination of individual grunt waveforms showed variation in apparent modes of vibration corresponding to human phonation in the modal and pulse registers. LPC analyses revealed an overall spectral pattern approximating that of the vowel schwa. However, formant positions were found to vary to a greater degree among calls produced by different individuals than between communication contexts. This outcome suggests a low degree of flexibility in articulator positioning. Overall, baboon grunts acoustic features appear to reflect the action of a source-filter production system in which vocal tract filtering mainly provides cues to caller identity.
Competition and categorization: The effect of choice set on vowel category structure
Authors: Galama D. A. , Nearey Terrance M.
Published: October 2005

The effect of competition on the perception of category peaks and on goodness judgments was examined. A 48-step vowel continuum spanning the /I–ε–æ/ range was synthesized by varying F1 and F2. Subjects listened to multiple presentations of all 48 vowel stimuli in five separate conditions, with nature of the choice set as the dependent variable. The five choice sets were: /I–ε–æ/, /I–ε/, /ε–æ/, /I–æ/, and /ε/. For each of the first four conditions, subjects were asked to simultaneously categorize and provide category goodness ratings for the vowel stimuli. In the fifth condition, subjects were required to provide goodness judgments only, thereby indicating perceived degree of membership to the category /ε/. Identification and goodness functions corresponded well to each other, with changes in the competition paradigm affecting both of these functions similarly. Also, location of category peaks and range of goodness judgments exceeding 90% were found to remain relatively stable, regardless of the number of categories in the choice set. While the results of various normalization studies suggest that the structure and location of vowel category peaks is highly affected by various contextual factors, they appear to be relatively unaffected by the nature of category competition. [Work supported by SSHRC.]
Shallow-water acoustic measurements in the southern Adriatic Sea
Authors: Berkson J. M. , Hollett R. D. , Max M.
Published: October 2005

Shallow-water acoustic and geoacoustic measurements were made in the southern Adriatic Sea in May–June 1995 in combination with detailed oceanographic, geological, and geophysical surveys. Seismic subbotom profiling, narrow-beam echosounding, and bottom coring results were used to select two shallow water sites with downward refracting conditions for acoustic experiments: (1) a flat seafloor at 90-m depth with about 1 m of rigid, nongaseous clay over a sequence of laminated clays and (2) a seafloor sloping from 49- to 37-m depth and consisting of soft gaseous mud over laminated clay. Broadband sparker and 180-g TNT explosive sources were used for propagation and reverberation to a vertical array receiver in addition to cw sources for propagation. Initial results for the deeper water site show frequency-independent propagation that is consistent with modeled results using geoacoustic parameters extrapolated from coring results. A modification of the Dix method to estimate sediment sound speed versus depth from wide-angle reflectivity experiments made at the deeper water site is described. [Work supported by ONR.]
Seismoacoustic modeling of thin sedimented regions in the mid-Atlantic ridge
Authors: Chin-Bing Stanley A. , Murphy Joseph E.
Published: October 2005

In several previous meetings results have been reported comparing computer generated acoustic simulations with reverberation data taken from the mid-Atlantic ridge region during the 1993 Acoustics Experiment (‘‘Site A, Seg 076’’ from the ONR Acoustic Reverberation Special Research Program). The acoustic simulations used representations of the rough, range-dependent ocean sediment/subbottom bathymetry that were generated by geomorphology models (the Webb–Jordan sediment distribution model and the Goff–Jordan fractal seafloor/basement model). A modified version of the Collins FEPE2WAY model was used for the long-range reverberation predictions. The simulated backscatter signal (210–280 Hz) compared favorably, in structure and level, with the reverberation data. In this study the same PE model is used to propagate the incident field to a thin sedimented region of interest. This field is then used as the initial field to the FFRAME and SAFE models to study the seismoacoustic influence of the thin sedimented regions on reverberation. Results will be presented that indicate the effects that shear waves and shear wave attenuations have on the reverberation. [Work supported by Office of Naval Research, Acoustic Reverberation SRP, and a High Performance Computing DoD Shared Resource Center grant.]