bluuebunny/crossref_metadata_2025 huggingface dataset:
Sound scattering from near-surface bubble clouds
Authors: Schindall Jeff , Carey William M. , Roy Ronald A. , Crum Lawrence A. , Nicholas Michael
Published: October 2005

Recently an experiment was conducted to measure sound scattering from submerged bubble clouds generated in a fresh water lake at a depth of 87.5 m [Roy etal., J. Acoust. Soc. Am. 91, 2314(A) (1992)]. These clouds, which consisted of bubbles with a mean radius of 1.1 mm, were roughly cylindrical in shape with a nominal radius and length of 0.5 and 1.5 m, respectively. The backscatter target strengths measured below 1 kHz were large−of order 0 dB. Although the bubble size distributions were larger than those observed in the open ocean, these measurements, nevertheless, demonstrate the collective behavior characteristic of small bubbles occupying an acoustically compact space. This paper briefly reviews these experimental results and compares the acoustic characteristics of our clouds with those generated by breaking waves at sea. First, the dispersion curves and damping characteristics for these clouds are presented. Second, calculations for spherical and cylindrical clouds showing the scattering characteristics from the low to high frequencies are presented. Finally, the effect of the rough sea surface is estimated. [Work supported by ONR, ONT, AEAS, and NUSC/IR.]
Sound scattering by zooplankton with arbitrary shape and orientation
Authors: Chu Dezhang , Stanton Timothy K.
Published: October 2005

One of the challenges in describing the sound scattering by finite elongated objects with applications to zooplankton lies in the complexity of their shape and physical properties. Several approximate models have been developed to date in this field including deformed cylinder model, which allows the cross section of the scatterer to vary along its elongated axis [T. K. Stanton, J. Acoust. Soc. Am. 86, 691–705 (1989)]. While valid for a wide range of material properties, this model is restricted to a normal or near normal incident wave and requires a target to have a high aspect ratio. In this study, taking advantage of the fact that many zooplankton can be approximated as weak scatterers, a distorted wave Born approximation can be applied to compute the backscattering from such scatterers. Different from the conventional Born approximation, a substitution of the internal field by the incident field with a modified phase is used to obtain the backscattered field expressed explicitly as a volume integral over the entire body of the scatterer. This model can be applied to more complicated shapes with arbitrary orientations and its validity has been tested for various cases in which the exact solutions exist. Comparisons with data are made. [Work supported by ONR.]
Reflection and diffraction from a disk: A look in the time domain
Authors: Norton Guy V. , Keiffer R. , Novarini Jorge C.
Published: October 2005

The classical problem of sound scattering from an infinitesimal thin disk is re-examined in the time domain via Fourier synthesis of solutions calculated, in the frequency domain, through a T-matrix formalism. Two T matrices were used. The first was specifically developed for the disk, the second was more general in that it allowed a sphere to be transposed into an oblate spheriod, where in the limit that the length of the semi-minor axis goes to zero produces an infinitesimal thin disk. At difference from the frequency domain, once the solution is mapped onto the time domain, diffracted and reflected components of the scattered field are clearly separated. In this work this feature is used to analyze the relative strength of the different component of the impulse response, for the case of an acoustically rigid disk (Neumann boundary condition), and an acoustically soft disk (Dirichlet boundary condition). A point source is assumed, and the analysis is restricted to normal incidence. Results are compared with predictions from a Helmholtz–Kirchhoff solution. The main findings are that, while the reflected components of the hard and soft disks differ only in their sign (as predicted by Kirchhoff theory), the relative strengths of diffractions and reflections are drastically different for the two cases. Furthermore, for the hard disk secondary diffraction is clearly identified in terms of Huygens contributions, while no counterpart is observed for the soft disk. In addition, results from the oblate spheroid approaching the disk will be shown.
On the benchmarking of the extended wedge assemblage method: Scattering from a thin disk
Authors: Keiffer Richard S. , Novarini Jorge C. , Norton Guy V.
Published: October 2005

The so-called wedge assemblage (WA) method was originally benchmarked for 1-D gratings [Novarini etal., J. Acoust. Soc. Am. 77, 1754–1759 (1985)], and later extended to 2-D surfaces [R. Keiffer etal., ComputationalAcoustics, Vol. 1, IMACS (1990)]. For either case, the exact time domain solution by Biot and Tolstoy for an infinite wedge is the starting point for the modeling of scattering from more complex surfaces. The main hypothesis involved in the extension of the WA method to surfaces that are not corrugated or long-crested is based on experimental observations [H. Medwin, J. Acoust. Soc. Am. 69, 1060–1064 (1981)] that the diffracted response of a truncated wedge is equal to the appropriately time-windowed response of equivalent infinite wedge. In this paper this hypothesis is tested for a scattering surface (the thin disk) for which the implementation of the extended WA method is conceptually simple yet, particularly for monostatic scattering at normal incidence is very demanding. As a benchmark, a T-matrix approach is adopted and Fourier transformed to the time domain for comparisons with the WA results. Both Dirichlet and Neumann boundary conditions are examined.
Computational aspects of immersive acoustical environments
Authors: Sawhill Bruce K.
Published: October 2005

The importance of the auditory channel in creating realistic virtual environments has emerged as being of comparable importance to the much better understood visual channel. The auditory channel presents special computational challenges because of bandwidth and update rate requirements. So far, this has limited the synthesis of virtual sound to sound placement of multiple sources using head-related transfer functions (HRTFs), acoustical ranging, and simple echo processing using ray-tracing techniques borrowed from the field of graphics. Recent advances in microprocessor technology coupled with advances in computational algorithms have brought the possibility of true 3-D sound field synthesis to the fore. The essential advance required to make such a synthesis possible is the real-time diffractive treatment of sound. The mathematics and digital signal processing of diffractive sound is discussed, along with possible applications. [Work supported by the Human Interface Technology Laboratory, University of Washington, Seattle.]
A convolutional model for simulating the response of an electro-acoustic system inside a hall
Authors: Vogel Peter , de Vries D.
Published: October 2005

In a hall that is equipped with an electroacoustic system (EAS) for the enhancement of reverberation, the reflected sound field is built up by contributions of both system and hall. To quantify the transmission of the sound field from source to listener, from source to EAS microphones, and from EAS loudspeakers to listener, the appropriate hall transfer function should be taken into account. Also, the acoustic coupling between EAS microphones and loudspeakers may play an important role. In this paper, a convolutional model to calculate the complete hall and EAS response will be discussed, using a version of the image source algorithm that can also handle diffuse reflection at room boundaries. The EAS is divided in an early reflection module and a reverberation module. Examples will be shown, ranging from simple situations to complex configurations. Results are in good agreement with measurements.
Wave-front synthesis: A new direction in electroacoustics
Authors: Berkhout A. J.
Published: October 2005

The acoustics in auditoria is determined by the properties of both direct sound and reflections. If electroacoustic means are used to optimize the acoustics, one has to cope with unfavorable side effects such as localization problems and artificial impression of the reverberant field. To avoid those side effects, the concept of electroacoustic wave-front synthesis is introduced. The underlying theory is based on the Huygens–Rayleigh integral. In this concept, the wave fields of the sound sources on stage are measured by directive microphones; next they are extrapolated by means of an electronic processor, and finally, they are re-emitted in the hall by one or more loudspeaker arrays. Depending on the processor design, the wave-front systems can be used for direct sound enhancement, for simulation of discrete early reflections, or for generation of reverberation. Application of the wave-front synthesis concept also opens the door to a new approach of sound recording and reproduction.
Localization of moving reinforced sound source by superposed spread spectrum reference signal
Authors: Makino Tadayori , Riko Yasuhiro
Published: October 2005

A localization of moving reinforced sound source is described. A sound reinforcement system, in which microphones and loudspeakers are installed in the same sound field such as a conference room, has a drawback of insufficient reproduced sound pressure due to an adjustment to prevent howling. The fundamental technique of howling suppression that decreases coupling between microphones and loudspeakers is well known. The algorithm for decreasing coupling proposed here is based on a synthesis of directivity of microphone arrays to meet its dips in the directions of loudspeakers automatically. The direction of loudspeaker includes not only direct propagation but propagation through reflection and diffraction. In order to localize the direction in real time, a reference signal that is superposed on the speech signal is continuously detected by microphone. As a result, the reference signal whose sound pressure is low enough to be the same as the room noise of a typical broadcasting studio, will be detected without interference for speech communication by using spread spectrum technology.
EUROMET survey of European calibration facilities for underwater acoustics
Authors: Preston Roy C. , Robinson Stephen P.
Published: October 2005

EUROMET is a formal structure of contacts between National Metrology Institutes in Europe aimed at enhancing collaboration and coordinating research into new and improved measurement standards. A EUROMET project was established to undertake a survey of underwater acoustical calibration facilities with particular emphasis on primary standards and methods of dissemination. The results of the survey have been published in a report available from NPL [S. P. Robinson and R. C. Preston, RSA(EXT)32 (April 1992)]. This report lists the 64 organizations that provided information for the survey and describes facilities existing in each of the 17 participating countries. One of the findings of the study is that the concepts of primary and secondary standards and the associated methods of dissemination to users are not as well developed in underwater acoustics as they are in other fields of metrology, e.g., in the measurement of air-borne sound. Nevertheless, there is considerable activity in the field, and assuring the quality of measurements is now realized as being important in the move toward a single European market. A review of the concepts of measurement traceability as applied to underwater acoustics will be presented, together with an overview of the results of the EUROMET study with special emphasis on the UK facilities.
Graphics tool for 3-D tongue modeling
Authors: Wu Chao-Min , Wilhelms Reiner
Published: October 2005

An X-window-based graphics tool was developed to load serial images of histological sections of tongue specimens from a fetus available in the OSU College of Medicine, to enter contours and fiber directions of both intrinsic and extrinsic tongue muscles, and to implement a 3-D reconstruction of the tongue based on the assumption of lateral symmetry of the human tongue. It allows interactive loading of scanned-in images and their displays, sketching and labeling of various anatomical structures, and saving the sketches to files. The 3-D display of the sketches serves to construct a network of nodal points for a finite element representation. The intrinsic properties of the tissue, such as fiber direction, affiliation of local fiber directions with muscle types are compiled for each finite element. This tissue representation will be used later for the finite element analysis to simulate the deformation and movements of the tongue. The overall purpose of this study is to develop a computer model to represent the anatomy of the vocal tract and to simulate its movements by solving the equations of motion based on continuum mechanics. [Work supported by the Whitaker Foundation.]
Finite element tongue model−Algorithms
Authors: Wilhelms Reiner , Wu Chao-Min
Published: October 2005

An algorithm has been implemented that can solve the equations of motion of an incompressible tissue that is able of active contractions in multiple directions. This algorithm is used for the construction of a three-dimensional computational model of the human tongue. In the model, muscle fibers are represented as vector fields in a reference configuration, and the equations of motion are formulated in that reference configuration. The finite element method is applied for the numerical approximation, using 8 node or 27 node elements (for linear or quadratic interpolation). The muscular stresses are computed with a simple model of muscle tissue, in which the active stress depends on activation parameters and on the elongation in the direction of the muscle fibers and its rate of change. The activation parameters change the constitutive equations of the tissue. Incompressibility during the deformation is maintained by using a reduced stress calculation in which the components of the stress tensor, which cause nonisocoric deformation, are subtracted from the stress tensor. [Work supported by the Whitaker Foundation.]
Numerical simulation of unsteady flow in the glottal constriction with moving boundaries
Authors: Alipour Fariborz , Ni Jun
Published: October 2005

The unsteady airflow in the larynx with moving boundaries was visualized using numerical simulation. By employing the method of computational fluid dynamics (CFD), a two-dimensional model of laminar flow in the glottal constriction was built considering the changes in the wall geometry with time at a given frequency. The glottal wall was approximated with two sinusoidal curves (one for inferior opening and one for superior opening) connected with a straight line. The height of the superior opening was changed as a sinusoidal function of time to generate the desired glottal wall movements. The Navier–Stokes equations with pressure boundary conditions was solved iteratively with the Phoenix CFD code. A shadow method with fixed grid points was used to avoid the complexities of the moving grids. Results were reported on the velocity pattern and pressure distributions at various time steps and also time variations of pressure and velocity at certain points were studied. The study provides a basis for further investigation of pulsatile flow in the larynx. [Work supported by NIDCD Grant No. DC00831-01A2.]
Modal analysis of a finite element simulation of the vocal folds
Authors: Berry David A. , Titze Ingo R. , Herzel Hanspeter , Krischer Katharina
Published: October 2005

A modal analysis is made of a biomechanical simulation of the vocal folds. The dominant modes of the finite element simulation are computed by performing a principal components analysis on the time-varying nodal coordinates of the model. For simulations of normal phonation, the model−which contains many degrees of freedom−is reduced to essentially two dominant modes corresponding to those predicted by Titze and Strong [‘‘Normal modes in vocal cord tissues,’’ J. Acoust. Soc. Am. 57, 736–744 (1975)]. Additional modes are needed to explain simulations of pathological voice. The dominant modes from the various simulations will be displayed and discussed. The ability of traditional vocal fold models to capture these modes will also be considered. [This research was supported by Grant No. P60 DC00976-0X from the National Institutes on Deafness and Other Communication Disorders.]
Effects of circumferentially moving loads on the vibration and sound radiation of finite cylindrical shells
Authors: Panneton Raymond , Berry Alain , Laville Frédéric
Published: October 2005

Sound radiation by circular cylindrical shells has been of interest for several years because this kind of structure is encountered in many products. Usually, the structures studied are circular cylindrical shells excited by stationary harmonic point loads. In the present case, a model is developed to calculate the vibrational response and sound radiation of a simply supported stiffened circular cylindrical shell excited by local or distributed circumferentially moving loads. This kind of system is a basic modelization of the ‘‘pressure screens’’ used in the pulp and paper industry. A variational approach is used to develop the analytical formulation to solve the problem. The results can be interpreted in terms of vibrational and acoustical parameters such as the quadratic velocity of the shell, the radiated sound power, and the radiation efficiency. Numerical results for various types of load and rotational speeds are presented and principal phenomena are discussed. Also, to validate the model, the theoretical results are compared to experimental results obtained for a simply supported cylindrical shell under circumferentially moving loads.
Reference models for fluid-loaded cylindrical shells excited by phased ring forces
Authors: Ricks David C. , Schmidt Henrik
Published: October 2005

A fluid-loaded cylindrical shell is modeled with the full equations of elasticity. The model is excited by time-harmonic ring forces that can push in the radial, circumferential, and axial directions. The ring forces can have a linear phase shift around the circumference of the shell, so helical waves can be excited and studied for any circumferential order. This ‘‘full elastic’’ model serves as a reference model to check the accuracy of the Donnell ‘‘thin shell’’ equations. When identical shells are excited by identical ring forces, the ‘‘full elastic’’ and ‘‘thin shell’’ models exhibit the same modes of wave propagation, with slightly different amplitudes of response. However, in some cases, the wave speeds are very different. The significance of these differences is being evaluated. [Work supported by ONR.]
Effective material properties of a hollow elastic sphere that undergoes a finite deformation under the action of external hydrostatic pressure
Authors: Rudgers Anthony J.
Published: October 2005

The analytic solution to the problem of the linear, but finite, deformation of a hollow elastic sphere, occurring when the sphere is subject to external hydrostatic pressure, is described in this paper. In this problem, the theory of linear elasticity is considered to characterize incremental deformation of the hollow sphere, but, owing to the concomitant incremental change in geometry, the radial deformation of the sphere caused by a hydrostatic pressure of finite magnitude is a nonlinear function of that pressure. By calculating how a hollow sphere deforms with pressure, the effective bulk modulus and effective density of the sphere can be found as a function of hydrostatic pressure. These effective properties of hollow spheres would be needed if one wished to describe the acoustic behavior of syntactic-foam composite materials that incorporate hollow spheres as one of their constituents. [Work supported by ONR.]
A trajectory formation model of articulatory movements
Authors: Kaburagi Tokihiko , Honda Masaaki , Okadome Takeshi
Published: October 2005

The generation of articulatory movements suffers from the degrees-of-freedom problem in determining the phoneme-related shape of the vocal tract. This model is intended to study the coordinative movement of articulatory organs. The redundancies of the articulation system are solved by minimizing an appropriate objective function to determine articulatory movement uniquely. In the model, articulatory movements are represented as the output of a multi-dimensional second-order linear system driven by input forces. These movements are partially constrained by phoneme-related features of the vocal tract shape at given instants. The input forces are determined by minimizing the cost function, represented as the energy sum of the time-differentiated system inputs and outputs. Then, articulatory movements are obtained as the system response to the optimum inputs. The trajectory formation model is computer-simulated to generate tongue, lip, and jaw movements for VCV segments. Comparison of simulated trajectories with data measured using a magnetic position-sensing device shows that the model is able to generate accurate jaw–lip or jaw–tongue coproductions and anticipatory coarticulation for the segments.
Comparison of displacement thresholds in auditory and visual modalities
Authors: Ball Jennifer M. , Perrott David R. , Booth Geoff A. , Cisneros John
Published: October 2005

Previous research of moving sound sources show an increase of minimal displacements as a direct function of velocity. The current experiment attempted to establish upper limits for this function. Five subjects were tested, three naive and two experienced. MAMA thresholds for velocity ranging from 10 to 1500 deg per second were obtained using a three-up one-down adaptive procedure. For comparison purposes, visual targets were also employed in the paradigm. For velocities in excess of 100 deg per second, auditory displacement thresholds were substantially lower than those obtained for vision. However, the superiority of the visual modality was evident at lower rates of travel. These results will be discussed relative to our hypothesis that the auditory system may have a significant role in oculomotor processes.
Correlations between auditory and visual speech processing ability: Evidence for a modality-independent source of variance
Authors: Watson Charles S. , Qiu William W. , Chamberlain Mary
Published: October 2005

Two experiments were run to determine whether the individual differences in auditory speech processing are predictable from those in speechreading, using a total of 90 normal-hearing subjects. Tests included single words and sentences. The speech was recorded on a video disk by a male actor (Bernstein and Eberhardt, 1986, Johns Hopkins Lipreading Corpus). The auditory speech was presented with a white noise masker, at −7 dB Sp/N. The correlations between overall auditory and visual performance were 0.52 and 0.45, in the two studies, suggesting the existence of a modality-independent ability to perceive linguistic ‘‘wholes’’ on the basis of linguistic fragments. Subjects also identified printed sentences with 40%–60% of the portions of the letters deleted. Performance on that ‘‘visual-fragments’’ test also correlated significantly with visual and auditory speech processing. [Work supported by AFOSR, through a grant to the Institute for the Study of Human Capabilities.]
Modal analysis techniques applied to sound field representation
Authors: Hansen Uwe J. , Bork Ingolf
Published: October 2005

In structural dynamics, modal analysis permits normal mode representation for vibrating structures by recording multiple transfer functions and letting a computer animate a simple harmonic oscillator approximation to display normal mode motion in an expanded time frame. This work shows an example of applying this technique to the representation of a sound field. Phase information is recorded by using the excitation source as a reference signal, monitoring the sound field with a microphone, and forming a transfer function of the two with a dual channel FFT analyzer. The method is illustrated by showing the sound field above and below the sound board of a grand piano, and in a vertical plane in the general direction of an audience.
Symphonic bells of ‘‘fantastic’’ proportion
Authors: Caswell Daryl
Published: October 2005

Producing the sound of a large bell in an orchestral setting is considered to be one of the most significant unsolved problems of the percussionist. A real bell of the proper frequency range is too large to control in performance and too cumbersome to suspend or transport. The use of bell plates in place of actual bells has had limited success due to the difficulties encountered in producing accurate pitch, sufficient amplitude, and a reasonable frequency response. This paper is based on a novel, multidisciplinary approach that has resulted in the production of bell plates with marked improvement in the most problematic areas. The musical value of the research has been demonstrated by two bell plates designed to produce the sound of distant church bells in the final movement of Hector Berlioz’s SymphonieFantastique. The plates were used in performances by both the Calgary Philharmonic and the Vancouver Symphony.
A short multicomponent music test battery
Authors: Cohen Annabel J.
Published: October 2005

This half-hour battery, which included 16 subtests, examined lower- and higher-level perceptual/cognitive and affective responses to musical stimuli. A comparison of the results from two independent groups of university students revealed highly significant correlations between response patterns both over individual items and over subtests. The agreement between the two groups supports the feasibility of the short multicomponent test for providing a musical-abilities profile of diverse populations, and a potential screening and classification instrument for individuals. Although past music tests have been applied primarily within the domain of music education, recently several tests (e.g., Seashore MMT, Gordon MAP, and Gordon PMMA) have been employed in cognitive neuropsychology, music therapy, or audiological contexts for the purposes of understanding neurological function and determining effects of aging, hearing loss, and hearing assistive devices. The efficiency, breadth, and variety of the present test recommend it for similar research applications in which time for testing and attention span of the listeners may be greatly constrained. [Work supported by NSERC and SSHRC.]
Hierarchical event detection
Authors: Todd Neil P. McAngus
Published: October 2005

Research on musical performance has shown that expressive variations in tempo, dynamics, etc. not explioit in a score can be acounted for by structural factors such as phrasing and rhythm [N. P. McAngus Todd, J. Acoust. Soc. Am. 91, 3540–3550 (1992)]. There now exists a number of models that attempt to recover rhythmic structure from a performed sequence [H. C. Longuet-Higgins, Nature 263, 646–653 (1976); P. Desain, Music Percept. 9(4), 439–454 (1992)]. However, they do not address the question of how the human auditory system might detect temporal events before such higher level processing. A low-level representation is proposed, analogous to the primal sketch in vision [D. Marr and E. Hildreth, Proc. R. Soc. London Ser. B 207, 187–217 (1980)], enocoding intensity changes at different time scales via an array of filters tuned at very low infrasonic frequencies. This representation could act as a front end to perceptual models. Various outputs from an analog implementation of the filter array are demonstrated including music, speech, poetry, and bird song.
Special concerns of noise control on offshore platforms
Authors: Bommer Arno S. , Bruce Robert D.
Published: October 2005

Although much of the equipment used on offshore platforms is also used in onshore drilling and production facilities, the constrained site and unusual operating conditions result in a significantly different acoustical environment. Helicopter landing pads, flares, mud pumps, drawworks, gas turbines, generators, compressors, heaters, coolers, and cranes may all exist within 50 m of sleeping quarters. The density of equipment and piping make sound source identification and treatment difficult and the harsh environment and safety considerations result in stringent requirements for noise control treatments. Structure-borne noise paths are also a special concern. Case histories describing offshore platform noise measurements, noise modeling, and equipment noise control will be discussed along with a general overview of the different types of offshore platforms and the specialized equipment on the platforms.
Sound velocity and attenuation in crystalline C60
Authors: Shi X. D. , Chaikin P. M. , Kortan A. R. , Williams J. M. , Kini A. M. , Savall B. M.
Published: October 2005

A brief review is given on some of the most interesting structural and electrical properties in the C60 fullerenes. The elasticity study is reported on for C60 single crystals of different lattice symmetries. The temperature dependence of the sound velocity in the fcc crystals shows a discontinuous jump corresponding to about 8% increase in the modulus at an orientational ordering transition temperature T=260 K. This large change in the elastic modulus indicates a drastic change in the interaction mechanism between the molecules. At T∼160 K, the sound velocity is observed to increase considerably accompanied by a profound peak in the sound attenuation whose position is frequency dependent. The 160 K anomaly is associated with relaxations of the C60 molecules to symmetry-inequivalent orientations in response to the stress field with the characteristic relaxation frequency following an activated temperature dependence and coinciding with the measurement frequency of about 20 kHz around 160 K. In the monoclinic crystals, the orientational ordering transition takes place at 242 K and is of second-order nature, while the 160 K freezing process remains unchanged.
Acoustoelectric interaction in high T
c films
Authors: Levy Moises
Published: October 2005

Surface acoustic wave (SAW) may acoustoelectrically interact with a superconducting film deposited on the surface of the piezoelectric substrate which carries the SAW. The polarization fields accompanying the SAW induce currents in the normal conducting film producing attenuation via Ohmic losses which are subsequently quenched when the film becomes superconducting. In a homogeneous film, the SAW attenuation will be proportional to the resistivity of the film even through the superconducting transition. In a granular film percolation effects broaden both the resistive and attenuation transitions. However, if the number of grains per SAW wavelength is sufficiently small, then the attenuation transition is broadened even more than the resistive transition, and the acoustoelectric attenuation in the normal state is larger than it would be for a homogeneous film with the same sheet resistivity. An acoustoelectric attenuation percolation model has been developed which may yield information about the granularity of the film being measured, or conversely if the granularity is known from other techniques, it is possible then to estimate the resistivity of the individual grains composing the film. In the case of the high Tc film that has been measured, this turns out to be 12.5 μΩ cm for grains whose dimensions are about 3000 Å. [This research was supported by ONR.]
Newborn discrimination of speech-like sounds
Authors: Shoup-Pecenka Angela G. , Walton Gail E. , Bower N. J. A. , Bower T. G. R.
Published: October 2005

Knowledge of the development of auditory sensation and perception is of unquestionable theoretical and practical importance. A procedure for behaviorally assessing auditory perception in newborns, based on sucking, has been developed. Neonatal thresholds to tonal stimuli, obtained with this measure, have been reported [A. G. Shoup-Pecenka etal., J. Acoust. Soc. Am. 90, 2297 (A) (1991)]. For the present study, speech discrimination thresholds were assessed in the well-baby nursery of a county hospital. The stimuli used were a forward English /u/ and the same sound played backward, at various intensities (0, 5, 10, 15, and 20 dB re:normal adult threshold). These stimuli were chosen because newborns have been reported to discriminate between them at a suprathreshold level [A. Weintraub, 8th International Conference on Infant Studies (1992)]. Using a procedure similar to the one for obtaining tonal thresholds, the level at which the neonate could determine the difference between two speech sounds was determined and compared to the infant’s 1–3 kHz threshold. Results suggest that speech discrimination thresholds for newborns are comparable to those for adults.
Classification of fibers innervating the cat hindpaw
Authors: Checkosky Christin M. , Bolanowski Stanley J.
Published: October 2005

Neural responses were recorded from fibers innervating the glabrous skin of the cat hindpaw to determine if the preparation can be an adequate physiological model for human glabrous skin. Adaptational properties, receptive field (RF) organization, and intensity (IC) and frequency (FC) characteristics of fibers (n≳116) in the medial plantar nerve were obtained in response to sinusoidal vibrations. The fibers could be grouped into four categories similar to those found for fibers innervating human glabrous skin: (a) Pacinian corpuscle fibers (22.2%) having large RFs, fast adaptation, U-shaped FCs in the 40–400 Hz range, and ICs showing plateaus at multiples of the stimulus frequency; (b) rapidly adapting fibers (22.2%) having small receptive fields, fast adaptation, U-shaped FCs in the 10–150 Hz range, and ICs showing plateaus; (c) slowly adapting type I fibers (20.0%) having small RFs, slow adaptation, positive sloping FCs in the 10–150 Hz range, and ICs showing plateaus; and (d) slowly adapting type II fibers (35.6%) having large RFs, slow adaptation, negative sloping FCs in the 20–300 Hz range, ICs without plateus, and low-rate spontaneous activity. [Work supported by NIH Grant Nos. DC00380 and DC00098.]
Mean energy calculations in a numerical parabolic equation average propagation method
Authors: Oba Roger M.
Published: October 2005

A computational method of numerically computing average pressure has been developed using a normal mode analysis of the parabolic equation [R. M. Oba, J. Acoust. Soc. Am. 91, 2424 (A) (1992)]. It has been implemented to compute the transmission loss and phase for the average solutions in the continuous wave case. Time domain cases have been computed by Fourier transform. This analysis can be extended to compute the average energy over the ensemble at a given range in the continuous wave case. Since energy is positive for each element of the ensemble, the calculation of its mean will obviate the larger transmission loss due to phase cancellation in ensemble averaging of the complex valued solutions. Comparison of average energy calculations can be made to the energy of the average solution. This technique will be useful in matching this computed field at some final range to another solution starting from that range on. [Work supported by ONR/NRL-SSC and ONR Young Navy Scientist Program.]
Geometric beam tracing
Authors: Liu Yong-Chun , Porter Michael B.
Published: October 2005

Despite their approximate nature, ray methods continue to play an important role in ocean acoustic modeling−sometimes there is no practical alternative, for instance, in modeling impulses or high-frequency sources in 3-D environments. Unfortunately, ray methods are prone to implementation difficulties which often degrade their accuracy. Problems include the failure to locate an eigenray (leading to artificial drop-outs), errors in tracking the phase change through a caustic or singularities at caustics. Gaussian beam methods have been proposed as a remedy; they lead to particularly simple codes free of these problems. However, the promise of Gaussian beam methods remains partially unfulfilled since the optimal choice of beam initial conditions is still being debated. A modified beam tracing algorithm is described that preserves the appealing structural simplicity of Gaussian beam tracing but sacrifices the caustic correction to obtain a robust algorithm. Plots of transmission loss show that the resulting model yields excellent agreement with more computationally intensive full-wave models.
Combination of Gaussian beam optimization and finite element method in describing underwater distributed source sound field in an inhomogeneous medium
Authors: Huang Dehua , Breazeale M. A.
Published: October 2005

A non-Green’s function integral method−the Gaussian beam optimization superposition representation [Wen and Breazeale, J. Acoust. Soc. Am. 83, 1752–1756 (1988)], combined with the finite element solution to the parabolic wave equation [Huang, J. Acoust. Soc. Am. 84, 1405–1413 (1988)], has been developed to treat the underwater diffraction field of a distributed source. The numerical examples cover Gaussian and multiple Gaussian sources, homogeneous and inhomogeneous media, high- and low-frequency range, and regular or irregular interface boundaries.
Multiple precursors due to leaky head waves
Authors: Smith Kevin B. , Tappert Frederick D.
Published: October 2005

Using the parabolic approximation to the wave equation, the influence of head wave propagation along the water–sediment interface on the total field in a range-independent environment can be computed analytically. Results from a numerical PE model are observed to agree nicely with the analytical solution for cw sources. The PE model may therefore be used with confidence to investigate various phenomena associated with head wave effects. A simple travel-time geometrical model can be used to demonstrate that multiple arrivals in the time domain appear ahead of the direct path in the water column due to leaky head waves reflected by the sea surface back to the bottom at the critical angle. A broadband implementation of the PE model in shallow water numerically predicts these precursors quite accurately. Such precursors may not be easily distinguishable in practice and could lead to erroneous estimations of sediment sound speed. The effects of bottom loss and bathymetric range dependence has been investigated. Possible experimental configurations for observing these multiple precursor arrivals are suggested. [Work supported by ONR, Code 11250A.]
Efficient computation of synthetic seismograms in piecewise continuously layered fluids
Authors: Mourik Johannes P. L. , Tijhuis Anton G. , De Hoop Maarten V.
Published: October 2005

An efficient numerical scheme is presented for generating synthetic seismograms in continuously layered fluids with a countable set of discontinuities. The acoustic equations describing the wave propagation in such a configuration are subjected to a Fourier transform with respect to time and a Hankel transform with respect to the radial coordinate in the plane of symmetry. This reduces the scattering problem to a one-dimensional contrast integral equation over a finite domain, with a degenerate kernel. The latter equation must be solved for many values of the transform-domain variables. In view of this, a space discretization is introduced that is independent of these variables. The discretized form of the integral equation, inherent in a straightforward compression of the integral kernel, thus obtained is solved recursively with a procedure that closely resembles the invariant embedding technique. At each level, in the inhomogeneous medium, the outcome of the recursion can be converted into a transmission operator by a closing operation that represents the transition to a homogeneous half-space. The key advantage of this scheme is that discontinuities in the medium properties can be handled without special precautions. Further, it is shown that the inverse Hankel transform can be carried out with a specially designed composite Gaussian quadrature rule independent of frequency. Representative numerical results will be presented.
The maximal range step in parabolic wave propagation in shallow-water acoustics
Authors: Dannon Vic
Published: October 2005

To quickly obtain the wave field in parabolic wave propagation, this study sweeps the range in the largest possible range steps. Jensen and Krol [Saclanten Memorandum-72, NATO-SACLANTEN, La Spezia, Italy (1975)] obtained the truncation error of the parabolic equation that depends on the range step but did not derive the appropriate range step. The derivation was completed and it was implemented to a parabolic equation code. This study demonstrates that the truncation error of the parabolic wave equation is inadequate for the purpose of determining the maximal range step under acceptable wave-field error. This led to an analysis based on the truncation error of the wave field. It is shown that given a wave-field gain/loss of γ=10 log10‖η‖dB, the maximal range step Δr allowed is given by a formula that relates it to η (that measures the wave-field truncation error), the gradients of the refraction index n (with respect to range and height) and to the wave field and its gradients. The formula had been tested successfully on the parabolic equation code.
Viscosity of human bile and its role in gallstone lithotripsy
Authors: Everbach E. Carr , Vakil Nimish , Gracewski S. M.
Published: October 2005

Acoustic cavitation has been shown to play an important role in gallstone lithotripsy [Vakil etal., J. Acoust. Soc. Am. 90, 2340 (A) (1991)]. The bile surrounding a gallstone has been assumed to behave as a Newtonian fluid, with a viscosity independent of shear rate. Calculations show, however, that collapsing cavitation bubbles can produce shear rates nine orders of magnitude larger than those at which reported bile viscosities have been measured. Measurements of bile viscosity over a range of shear rates will be presented that show the non-Newtonian behavior of human bile, whose effective viscosity increases with shear rate. These results have implications for models of the behavior of collapsing cavitation bubbles during gallstone lithotripsy, and suggest the usefulness of clinical medical procedures that modify patients’ bile viscosity prior to lithotripsy.
Evolution of local spectra in smoothly varying nonhomogeneous environments−Local canonization and marching algorithms
Authors: Steinberg Ben Zion
Published: October 2005

A new wave equation that governs the evolution of local spectra of wave fields in a general nonhomogeneous environment is developed. The equation is obtained by applying the windowed Fourier transform directly to the Helmholtz wave equation. It is shown how simple analytical solutions of the new wave equation in a general smoothly varying nonhomogeneous environment can be obtained using well-known analytical techniques, and how the marching methodology connects these new solutions to the original problem described by the Helmholtz equation.
The application of a normal mode perturbation method to assess the effects of sound-speed fluctuations on the propagation of narrow- and broadband acoustic energy in the sea
Authors: Ali Hassan B. , Werby Michael F. , Broadhead Michael K.
Published: October 2005

Fluctuations in the intensity of an acoustic signal are a common feature of propagation of sound in the sea. The fluctuations are a manifestation of the temporal variability of the index of refraction (sound velocity) of the medium which, in turn, is induced by a variety of random and deterministic ocean processes covering a wide spectrum of temporal and spatial scales. In this paper, a recently developed high-order perturbation method is described and applied to the problem of sound propagation in the sea. The basis functions used in the calculations are derived from sound-speed profiles obtained in an acoustic propagation experiment conducted in a shallow-water region of the Mediterranean. Each profile is treated as a perturbation from a mean profile, the latter obtained by depth-averaging the profiles. At particular source frequencies, calculations of modal functions and acoustic transmission loss were compared for the mean and several perturbed profiles. These initial discrete-frequency results were presented at the Scintillations Conference (University of Washington, Seattle, Washington, August 1992). Here, the method is extended to include the response of broadband, transient sound sources and sources at several water depths. The broadband (time-domain) approach enables one to readily determine the optimum frequencies of the shallow-water duct and, in addition, to assess the effect of sound-speed fluctuations on the optimum frequencies. These results, along with the earlier ones, confirm the significant effects on acoustic transmission of seemingly minor variations in sound speed and, moreover, demonstrate the efficacy of the new perturbation method in handling such problems.
Environmental perturbation of ocean waveguide eigenmodes
Authors: McDonald B. Edward
Published: October 2005

Explicit forms are derived for the coupling matrix that relates perturbations in environmental parameters to resulting perturbations in the trapped acoustic modal eigenfunctions in the ocean waveguide [Kuperman etal., J. Acoust. Soc. Am. 89, 125–133 (1991); Desaubies etal., J. Acoust. Soc. Am. 80, 1148–1160 (1986)]. Special consideration is paid to the continuity conditions across the ocean/bottom interface. The perturbation is carried out with respect to frequency, ocean depth, sound-speed profile, and density distribution. Density is included to account for stratification in the bottom, and to estimate scattering from internal gravity waves near the thermocline. The matrix elements are expressed in terms of inner products of the unperturbed eigenfunctions with environmental perturbations. The results give straightforwardly the perturbations in eigenvalues (i.e., the horizontal component of the local wave vector for each mode). Applying the results to the variation of eigenmodes with horizontal position in the ocean, one finds separate terms for bathymetric (bottom slope) and oceanographic (water column) contributions. Results are related to the determination of horizontal ray paths of the trapped modes in global scale ocean acoustic experiments, and to the inversion of group arrival time data.
Predictability of low-frequency acoustic propagation in shallow, sloping bottom channels
Authors: Cederberg R. J. , Siegmann W. L. , Jacobson M. J. , Carey W. M.
Published: October 2005

The accuracy of PE model predictions for frequencies below 100 Hz in shallow-water channels with sloping bottoms is investigated. Comparisons are made among adiabatic approximations of analytic solutions to the Helmholtz equation and a wide-angle PE for two-layer isospeed sloping channels, an exact solution to the Helmholtz equation in a wedge, and predictions from the IFD implementation of the wide-angle PE. Inaccuracies due to the parabolic and adiabatic approximations are shown to be generally small for cases considered. Accuracy restrictions imposed by uncertainties of environmental and acoustic parameters are determined by observing changes in intensity and horizontal wave numbers caused by parameter variations in one adiabatic model. Range dependence of wave numbers is determined and methods for comparing these wave numbers are considered. Sensitivities of parameters such as sound speeds and bottom density are found to be similar to those from an earlier investigation of a flat bottom model [J. Acoust. Soc. Am. 89, 1896 (A) (1991)]. Parameter values and magnitudes of variations are selected consistent with a recent New Jersey shelf experiment. Comparisons of the experimental results with model predictions are discussed. [Work supported by ONR.]