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Feb 2006

Volume 119, Issue 2, pp. 669-EL19

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A numerically accurate and robust expression for bistatic scattering from a plane triangular facet

Gorm Wendelboe, Finn Jacobsen, and Judith M. Bell

J. Acoust. Soc. Am. Volume 119, Issue 2, pp. 701-704 (2006); (4 pages)

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This work is related to modeling of synthetic sonar images of naval mines or other objects. Considered here is the computation of high frequency scattering from the surface of a rigid 3D-object numerically represented by plane triangular facets. The far field scattered pressure from each facet is found by application of the Kirchhoff approximation. Fawcett [J. Acoust. Soc. Am. 109, 1319–1320 (2001) ] derived a time domain expression for the backscattered pressure from a triangular facet, but the expression encountered numerical problems at certain angles, and therefore, the effective ensonified area was applied instead. The effective ensonified area solution is exact at normal incidence, but at other angles, where singularities also exist, the scattered pressure will be incorrect. This paper presents a frequency domain expression generalized to bistatic scattering written in terms of sinc functions; it is shown that the expression improves the computational accuracy without loss of robustness.
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43.20.Fn Scattering of acoustic waves
43.20.Px Transient radiation and scattering

Geometric sound propagation through an inhomogeneous and moving ocean: Scattering by small scale internal wave currents

John A. Colosi

J. Acoust. Soc. Am. Volume 119, Issue 2, pp. 705-708 (2006); (4 pages) | Cited 1 time

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Ray equations appropriate for ocean acoustic propagation through an inhomogeneous and moving ocean are put forth with applications to sound scattering by internal waves. The result reveals the important role played by range dependent horizontal current shear. The Garrett–Munk internal wave model and observations of upper ocean shear and sound speed fluctuations suggest that inertial frequency upper ocean shear may play a comparable role to internal wave induced sound speed fluctuations as a source of upper ocean acoustic scattering.
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43.30.Cq Ray propagation of sound in water
43.30.Ft Volume scattering
43.30.Es Velocity, attenuation, refraction, and diffraction in water, Doppler effect

Confirmation of the Biot theory for water-saturated sands at high frequencies and effects of scattering on the attenuation of sound waves

Keiichi Ohkawa

J. Acoust. Soc. Am. Volume 119, Issue 2, pp. 709-711 (2006); (3 pages) | Cited 3 times

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Sound attenuation caused by the absorption and scattering of energy is studied. The Biot theory is used to predict the absorption coefficient. The scattering attenuation applies the experimental result. The calculated attenuation coefficient is the sum of absorption and scattering components, and is in excellent agreement with data collected during the sediment acoustics experiment in 1999. This implies that the frequency dependence of the attenuation coefficient due to the fluid viscosity follows f1/2 in the high-frequency range, as the Biot theory predicts. This also suggests that, at high frequencies, the attenuation coefficient is not linear in f.
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43.30.Ma Acoustics of sediments; ice covers, viscoelastic media; seismic underwater acoustics
43.30.Ky Structures and materials for absorbing sound in water; propagation in fluid-filled permeable material

Comment on “The cochlear amplifier as a standing wave: ‘Squirting’ waves between rows of outer hair cells?” [J. Acoust. Soc. Am. 116, 1016–1024 (2004)]

Eric L. LePage

J. Acoust. Soc. Am. Volume 119, Issue 2, pp. 712-714 (2006); (3 pages)

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Bell and Fletcher [ J. Acoust. Soc. Am. 116, 1016–1024 (2004) ] proposed that one of the functions of activity of the outer hair cells (OHCs) might be a fluid-pumping action generating lateral fluid flow in the gap between the reticular membrane and the tectorial membrane and they supplied mathematical and descriptive justification for their theory which drew heavily upon the postulation (Gold, 1948) of the need for an active mechanism in the mammalian cochlea. In the 1970s there had been considerable speculation about how the inner hair cell (IHC) stereocilia are stimulated, whether they are stimulated in proportion to basilar membrane displacement or velocity or both, and whether the velocity dependence is due to subtectorial fluid flow. In 1977 experiments were conducted to investigate the possibility of subtectorial fluid flows using a dye as tracer. The work was not reported because it had been conducted at a time when visual observation of cochlear function had fallen out of favor in comparison with the more sensitive techniques thought necessary to observe submicroscopic phenomena, and secondly because it yielded a negative result. The essential details of those experiments are reported here to note for the record the extent to which this elaborate idea has already been tested.
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43.64.Bt Models and theories of the auditory system
43.64.Kc Cochlear mechanics

Technique for “tuning” vocal tract area functions based on acoustic sensitivity functions

Brad H. Story

J. Acoust. Soc. Am. Volume 119, Issue 2, pp. 715-718 (2006); (4 pages) | Cited 7 times

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A technique for modifying vocal tract area functions is developed by using sum and difference combinations of acoustic sensitivity functions to perturb an initial vocal tract configuration. First, sensitivity functions [e.g., Fant and Pauli, Proc. Speech Comm. Sem. 74, 1975] are calculated for a given area function, at its specific formant frequencies. The sensitivity functions are then multiplied by scaling coefficients that are determined from the difference between a desired set of formant frequencies and those supported by the current area function. The scaled sensitivity functions are then summed together to generate a perturbation of the area function. This produces a new area function whose associated formant frequencies are closer to the desired values than the previous one. This process is repeated iteratively until the coefficients are equal to zero or are below a threshold value.
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43.70.-h Speech production
43.70.Bk Models and theories of speech production

Absolute pitch among American and Chinese conservatory students: Prevalence differences, and evidence for a speech-related critical period

Diana Deutsch, Trevor Henthorn, Elizabeth Marvin, and HongShuai Xu

J. Acoust. Soc. Am. Volume 119, Issue 2, pp. 719-722 (2006); (4 pages) | Cited 38 times

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Absolute pitch is extremely rare in the U.S. and Europe; this rarity has so far been unexplained. This paper reports a substantial difference in the prevalence of absolute pitch in two normal populations, in a large-scale study employing an on-site test, without self-selection from within the target populations. Music conservatory students in the U.S. and China were tested. The Chinese subjects spoke the tone language Mandarin, in which pitch is involved in conveying the meaning of words. The American subjects were nontone language speakers. The earlier the age of onset of musical training, the greater the prevalence of absolute pitch; however, its prevalence was far greater among the Chinese than the U.S. students for each level of age of onset of musical training. The findings suggest that the potential for acquiring absolute pitch may be universal, and may be realized by enabling infants to associate pitches with verbal labels during the critical period for acquisition of features of their native language.
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43.75.Cd Music perception and cognition
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