bluuebunny/crossref_metadata_2025 huggingface dataset:
Intracellular studies in eat cochlear nucleus: Physiological responses of morphologically identified neurons
Authors: Britt Richard H. , Rossi Glenn T. , Merest D. Kent , Ostapoff Michael
Published: October 2005

Intracellular recording techniques were used to study the physiological responses of cochlear nucleus neurons in 32 pentobarbital anesthetized cats. Electrodes were filled with 2% to 4% horseradish peroxidase (HRP) in 0.5 M KCl. Each neuron was studied extracellularly by obtaining a tuning curve, determining the characteristic frequency (CF), and generating a peristimulus time histogram (PSTH) at the CF. After intracellular penetration, the PSTH at the CF was repeated to determine if any change in response had occurred. HRP was then iontophoretically injected intracellularly. Serial transverse frozen sections were incubated using a diaminobenzidine reaction intensified by preincubation with cobalt chloride. In the anteroventral cochlear nucleus (AVCN), three HRP-filled neurons were physiologically characterized. A bushy cell located in the AA region had a primarylike response at its CF of 4 kHz. An elongated stellate cell in the PD region of the AVCN had a primarylike response at its CF of 10 kHz at 90 dB, but at lower intensities (80–60 dB) the unit showed a progressive change to a chopperlike response. A small stellate cell along the medial border of PV in the AVCN showed an onset response at its CF of 4 kHz. In the dorsal cochlear nucleus (DCN), a horizontal giant cell showed a change from an onset pattern below its CF to an onset-sustained pattern at its CF of 10.5 kHz. The second HRP-marked cell in the DCN was a small broadly tuned (7–18 kHz) granule cell recorded in the molecular layer which showed a primarylike response at its CF of 14 kHz. [Support: NIH/NINCDS NS15860.]
Hearing impairment and the masking-level difference in wideband and narrow-band masking noise
Authors: Hall Joseph W. , Haggard Mark P. , Harvey Anthony D. G.
Published: October 2005

The masking-level difference (MLD) was investigated for normal-hearing and cochlear hearing-impaired listeners. A 500- or 2000-Hz signal was detected in wideband noise (spectrum level 50 dB/Hz) and in a 50-Hz-wide noise around the signal frequency (spectrum levels of 50 and 60 dB/Hz). At 500 Hz the hearing-impaired listeners had appreciably smaller MLDs than normal in wideband noise, but normal MLDs in narrow-band noise. At 2000 Hz, the only condition in which the impaired group had abnormally small MLDs was the narrowband noise condition at the 50-dB/Hz noise spectrum level. The diagnostic and theoretical implication of these results will be discussed.
Intensity and duration effects in pure-tone frequency discrimination with normal-hearing and hearing-impaired listeners
Authors: Freyman Richard L. , Nelson David A.
Published: October 2005

Moore [J. Acoust. Soc. Am. 54, 610–619 (1973)] has suggested that under the assumptions of a place or excitation-pattern theory of frequency discrimination, frequency DLs should be dependent on auditory excitation-pattern slopes only for long-duration tones with spectral slopes that are steeper than those of the excitation pattern. Otherwise, according to this theory, it is the slopes of the stimulus spectrum that limit the frequency DL. In this paper, we extend these ideas to evaluate the prediction that for very short, spectrally broad tones, frequency DLs obtained from hearing-impaired subjects should not differ systematically from those obtained from normal-hearing listeners. Frequency DLs were obtained as a function of intensity at 500, 1000, and 2000 Hz for 5- and 300-ms pure tones in normal-hearing and moderately hearing-impaired subjects. The DLs obtained from hearing-impaired subjects were larger than normal for long-duration but not short-duration pure tones; these results are consistent with the predictions of the excitation-pattern theory. However, an unexpected but consistent finding of nonmonotonic frequency DL-intensity functions in the 5-ms condition in normal-hearing subjects complicates interpretations of the results.
Hearing losses in mongolian gerbil after 300 days of continuous exposure to noise
Authors: Mills John H. , Schmiedt Richard A. , Kulish Larry F.
Published: October 2005

As part of a large, long-term study of noise-induced hearing loss, pres-byacusis, and the interactions of the two, groups of mongolian gerbils are being exposed for their entire life to a wideband noise. The A-weighted sound pressure level is 85 dB. Control groups are being raised in an acoustic environment where the average sound level is less than 35 dBA. Hearing is estimated from electrical potentials arising from the auditory nerve and brainstem and recorded with noninvasive electrodes. Now, we report results from a pilot group of gerbils during the course of 300 days of continuous exposure to noise. Estimated threshold shifts were largest, about 40 dB, between 2 and 8 kHz and decreased at lower and higher frequencies. Threshold shifts at 4.0 and 8.0 kHz did not appear to increase (± 5 dB) between 30 and 300 days of exposure whereas at other test frequencies threshold shifts increased by as much as 20 dB between 60 days and 180 days. Aging control animals appear to develop hearing losses first at 16 and 20 kHz whereas noise-exposed animals develop their hearing losses first at 4 and 8 kHz. [Work supported by NIEHS.]
Plane-wave multiple-scattering approach to acousto-optic diffraction by adjacent ultrasonics
Authors: Banerjee P. P. , Chatterjee M. R. , Ponn T. C.
Published: October 2005

Plane-wave multiple-scattering theory has been used to analyze the diffraction of light by adjacent ultrasonic beams of frequency ratio 1:m. The novelty of the method lies in the fact that it provides a better physical insight into the actual coupling process involved in the generation of various diffracted orders than earlier, more conventional analtyical techniques; hence the resulting equations may be arrived at by simply inspecting the geometry of the problem and incorporating the appropriate phase factors contributing to each order. The analyses of acousto-optic diffraction by adjacent ultrasonic beams of frequency ratio 1:2 in the Raman-Nath and near Raman-Nath regimes are presented as illustrative examples. To compare with the work of earlier investigators, the variations of the scattered intensities are obtained numerically, for equal sound pressures in both columns, as a function of the phase difference between the beams and the strength of the sound fields for the first and second cases, respectively. The principle may readily be extended to more complicated sound-light configurations.
Exterior surface acoustic waves scattered by impenetrable cylinders
Authors: Gaunaurd G. , Brill D.
Published: October 2005

We study the scattering of acoustic waves by impenetrable (i.e., rigid and soft) cylinders by means of the poles of scattering amplitude that are present in the (nondimensional) complex-frequency plane, k1a. These are analogous to the poles that in electromagnetism are studied via the Singularity Expansion Method (SEM) of radar scattering. These poles correspond to external eigenvibrations of the medium surrounding the scatterers, which cause the external creeping waves that revolve around the targets, as we have already explained in detail [i.e., G. Gaunaurd et al., Nuovo Cimento 76B, 153–175 (1983)] for spherical scatterers. We have developed a formulation that permits the computation and display of the dispersion plots for the phase and group velocities and for the phase and group attenuations of the various orders of external creeping (Franz) waves revolving round these targets, directly from the positions of the SEM poles in the k1a plane. We show many such dispersion plots here as examples. We already showed [i.e., G. Gaunaurd et al., J. Acoust. Soc. Am. Suppl 1 72, S98 (1982)] how to compute the distortion of scattered δ-function pulses, incident on impenetrable spheres, by means of the stationary phase method, and we tie it all together here.
Power scattered by a fixed point on a fluid-loaded plate
Authors: Waterhouse R. V. , Archibald F. S.
Published: October 2005

When rectilinear bending waves on a thin plate encounter an obstacle in the form of a fixed point, some energy is scattered to the farfield. This scattered energy is the sum of two components, one traveling in the plate and the other in the fluid. The sum can be calculated from the real part of the driving point impedance imposed on a point-force driving the fluid-loaded plate. This impedance has been computed at various frequencies below the coincidence frequency, for a steel plate, 1 cm thick, loaded with water on one side. The impedance for the plate in vacuo is real and independent of frequency, but for the fluid-loaded plate, it is complex and frequency dependent. At each frequency, an integral representing a Hankel transform is evaluated numerically to yield the complex impedance.
Active sound intensity precision in a progressive and nonprogressive field
Authors: Nicolas J. , Lemire G.
Published: October 2005

The work is mainly dedicated towards the precision of the measurement of active sound intensity. The object is to describe the basis used to understand what is happening when measuring the sound power via the active part of sound intensity whatever the field is. The effects of acoustic center variation, of the phase mismatch, of the proximity of the source, of finite approximations, and of angle of incidence of the incoming wave are all combined in a general formulation, valid for the progressive field. The nonprogressive field is studied by calculating the estimated active sound intensity due to two monopoles. The case of coherent and incoherent monopoles are examined. A general formulation of the resulting amplitude and phase is developed and emphasis is put on a systematic parametric study of the theoretical phase gradient. The parameters are mainly the sound power ratio between the two sources, distance ratio, propagation difference, angle of incidence, and frequency. A formulation which allows us to calculate the precision between the estimated active sound intensity and the exact one is proposed. A criteria for evaluating the degree of nonprogressivity of the field will be discussed. [Work supported by the “Institut de Recherche en Santé et Sécurité du Travail.”]
Advances in nearfield acoustical holography (NAH) algorithms I. Green's functions
Authors: Veronesi William A. , Maynard J. D.
Published: October 2005

For efficiency, the spatial processing algorithms of NAH, based on Rayleigh's integrals, utilize the fast Fourier transform (FFT). In NAH, the FFT has been treated as an approximation to the continuous Fourier transform, and with this view, work has been done to reduce the errors introduced by the finite and discrete FFT. In this paper, it is shown that, by using the exact discrete convolution capabilities of the FFT and inverse FFT, as opposed to its approximate correspondence to the continuous Fourier transform, algorithms yielding more accurate results are obtained. The essential step is to replace the continuous field over the surface from which the data was gathered with a piecewise constant field, each patch having the constant field value as at a contained, measured point. With the field so replaced, Rayleigh's integral is reduced to a finite, discrete convolution of the measured data with the integrals of the kernel, or Green's function, over each path. Most importantly, this proces totally eliminates the effects of image sources. Conditions for validity of this model are presented, and results for a baffled piston source demonstrate the accuracy of this approach. [Work supported by ONR and NASA.]
Nearfield holography for wideband sources
Authors: Bowen Donald J. , Maynard J. D.
Published: October 2005

Nearfield acoustical holography (NAH), a process developed at the Pennsylvania State University, has proved itself to be a powerful research tool in the study of single-frequency sound sources. A new high-speed data aquisition system has been developed which permits extension of the nearfield acoustical holography technique to the study of wideband noise sources. Using a partially parallel, partially sequential sampling network, near simultaneous sampling is achieved for 256 microphones in the holographic measurement plane, for acoustic frequencies up to 1500 Hz. Special problems encountered during the development of the high-speed data aquisition system are discussed. [Work supported by ONR and NASA.]
Low-frequency, grazing propagation above randomly rough surfaces
Authors: D'Spain Gerald L. , Childs Emily H. , Medwin Herman
Published: October 2005

Previously we have summarized laboratory studies of the acoustic boundary wave due to coherent scattering at grazing propagation over surfaces with periodic roughness elements. Here we extend our study of low-frequency propagation for surfaces with three-dimensional, randomly rough elements [J. Acoust. Soc. Am. Suppl. 1 71, S24 (1982)]. The dependence of the boundary wave amplitude on scattering parameter, wavenumber, and range, εk3/2 r−1/2, predicted by Tolstoy for hemispheres, is found again for stochastic surfaces. However, the inferred scattering parameter can be an order of magnitude greater for sharp-edged than for spherical protuberances of the same volume/area. The empirical dependence of ε on the volume/area, rms slope, and rms curvature of the surface is examined. The maximum boundary wave amplitude again suffers catastrophic attenuation at a range and frequency given approximately by kr = 2π/(kε)2 as in the case of rigid spherical protuberances. The dispersion approaches 1%–2% at high frequencies and follows an approximate k2 dependence. [Research supported by the Offce of Naval Research.]
Double refraction near a rough bottom in isothermal waters
Authors: Medwin Herman , Novarini Jorge C.
Published: October 2005

The occurence of a boundary wave during low-frequency grazing scatter from rough rigid surfaces has been described by Tolstoy and experimentally verified by Medwin et al. [J. Acoust. Soc. Am. 66, 1131–1134 (1979)] for a homogeneous medium overlying the surface. Tolstoy [J. Acoust. Soc. Am. 69, 1290–1298 (1981)] has also shown that, when the velocity in the medium decreases away from the ocean bottom, tunneling into the shadow zone takes place, for source and receiver on the bottom. We re-examine this case but for the source and receiver near the ocean surface and for bottoms of lesser roughness. It is predicted that, under certain conditions of velocity gradient, frequency, and bottom roughness, the boundary wave mode causes a splitting of the limiting ray above the rough bottom. As a result, two refracted rays would reach the ocean surface: a primary ray (classical limiting ray for smooth bottom), and a secondary ray with a significantly greater skip distance. This double refraction phenomenon should be detectable at sea, under suitable experimental conditions. [Research supported by ONR.]
The T-matrix approach to scattering of waves by rough surfaces
Authors: Lakhtakia Akhlesh , Varadan Vijay K. , Varadan Vasundara V.
Published: October 2005

In this paper, we use the extinction theorem to compute a T matrix which characterizes a given rough interface between two media. In particular, we concentrate on multiple-layered geometries. Thus we consider an elastic rough infinite slab interfaced with different fluids on either side. This case serves as a model for studying water/ice plate/air systems. Numerical results illustrating the cases of longitudinal or shear wave incidence, as applicable, shall be presented.
Acoustic intensity from manganese nodule deposits
Authors: Ma Y. , Varadan V. K. , Varadan V. V.
Published: October 2005

Abundant information on manganese nodules in the deep ocean can be obtained from remote acoustic intensity measurements. The previously suggested low-frequency reflectivity measurements, neglecting the incoherent part of the backscattered acoustic signals, are quite good in predicting the presence of these nodules. However, in order to judge the effect of the size distribution on the acoustic response and to get the mean nodule size information, a wider frequency range is required. The contribution of the incoherent part of the acoustic response to the backscattered intensity becomes increasingly important as the sounding frequency gets higher. One may actually under-, or over-, estimate the amount of, and the average size of, the manganese nodules by carelessly neglecting the incoherent acoustic intensity. The intensity calculation based on the energy principle for nonabsorbing scatterers will be discussed, and the results will be presented for different concentrations of nodules with uniform as well as Rayleigh size distributions. All results presented shall be for sparsely distributed nodules made using the single scattering theory. The future extension to highly concentrated nodule fields by using the multiple scattering theory will also be discussed.
Backscattering from sub-bottom microlayers
Authors: Wyber Ronald J. , Muir Thomas G.
Published: October 2005

Vertical profiling measurements of the bottom in the frequency band from 1–5 kHz showed the variance of the reflected signal to be proportional to the frequency and the horizontal correlation length to be in the order of 10 m. This indicated that the variance in the backscattered signal is a function of the sonar beam pattern and the pulse shape, frequency, and grazing angle of the incident wave. For a pulse length of 25 ms and a grazing angle of 10°, the predicted backscattering strength was found to be independent of frequency at a level of −40 dB. This behavior agreed with data measured at this angle. As the classical theory of backscattering assumes that the bottom reverberation is due to independent scatterers which add incoherently, this theory will become invalid if the dimensions of the area ensonified on the bottom are less than the correlation length. Thus, for sonars with a short pulse or a narrow beam, the backscattered power will no longer be proportional to the ensonified area. [Work supported by the Office of Naval Research.]
Acoustic differential scattering cross section for internal waves
Authors: Bates Bruce J.
Published: October 2005

The Garrett and Munk internal wave field is a second-order process. It is also stationary, homogeneous, and anisotropic. Acoustic fields propagating through the internal waves are scattered by the internal wave sound speed fluctuations. The differential scattering cross section is derived employing the Born approximation and the “n frequency shell” condition. For comparison, the internal wave sound speed fluctuation is approximated by an anisotropic Gaussian correlation function and the resulting differential scattering cross section is evaluated for typical horizontal and vertical correlation lengths. Both differential scattering cross sections are compared as a function of scattering angle for selected angles of incidence and acoustic frequencies.
Acoustic propagation with an oceanic sound-speed model including a random field of internal waves
Authors: Bates Susan M.
Published: October 2005

Flatté and Tappert [J. Acoust. Soc. Am. 58, 1151–1159 (1975)] have shown that internal waves cause significant fluctuations in the transmission of acoustic energy through the ocean volume, comparable in size and frequency to the fluctuations observed in field experiments. They use the parabolic equation method to propagate acoustic signals. The random component of the sound-speed field is modeled by a linear superposition of internal wave eigenmodes. Each eigenmode amplitude is selected independently from a complex Gaussian distribution. Using an improved version of their simulation, range versus loss data are generated for up to 100 h of simulated time at 0.5-h intervals. The source of 100 Hz is located on the axis of the canonical profile. The ensemble average and variance of the acoustic signal, as a function of receiver location, are computed. [Work supported by NUSC.]
Sound scattering in a turbulent medium
Authors: Lataitis Richard J. , Crawford Greg , Clifford Steven F.
Published: October 2005

Tatarski [V. I. Tatarski, Wave Propagation in a Turbulent Medium (McGraw-Hill, New York, 1960)] has derived an expression for the effective scattering cross section of an acoustic wave incident on a remote volume of atomospheric turbulence. His result is subject to the single scatter approximation and the restriction that both transmitter and receiver be in the farfield of the large scale inhomogeneities within the volume. We derive an expression for the effective scattering cross section valid in both the near and farfield and extend these results to include the scatter of acoustic waves from underwater turbulence.
Near-range scintillations in a nonisotropic scattering medium
Authors: Frankenthal Shimshon
Published: October 2005

Using the Rytov approximation, an expression is derived for the log-amplitude correlation function of weak fluctuations induced in a plane wave propagating in a forward-scattering medium. The expression is valid at any range where weak fluctuations exist, including those which are shorter than the correlation length. The behavior of the scintillation index at very short ranges in isotropic media characterized by one or two scales is examined, and its dependence on frequency (k) and range (z) is listed for several regimes. Propagation is also studied in a nonisotropic medium, where the refractivity fluctuations are governed by the Garrett-Munk internal-wave spectrum. Here, the frequency-range dependence of the scintillation index changes from k3/2 z5/2 at very near ranges to kz2 at more distant ones.
Calculated and measured fish-school echoes
Authors: Ingalls Paul D.
Published: October 2005

A simulation model that generates the waveform of a high-frequency acoustic echo from a model fish school has been developed. The echo model generates the waveform by coherent addition of echoes from a collection of model point scatterers that have position, scattering amplitude, and velocity parameters chosen to reproduce some of the observable properties of echoes from real fish schools. Sample echo waveforms, spectra, and split-beam phase difference will be presented. This model has been used to show the effects of partial ensonification on apparent size and scattering parameters of fish schools. [Work supported by U.S. Navy.]
An overview of pattern recognition and its application in acoustics
Authors: Fu K. S.
Published: October 2005

The problem of pattern recognition is introduced and its major approaches briefly reviewed. In the decision-theoretic approach, both parametric and nonparametric classification techniques are described. In the syntactic approach, pattern description languages and their recognition algorithms are discussed. Application examples are presented. VLSI implementations of some of the techniques are discussed. A unified syntactic-semantic approach is then proposed. Problems for further study are suggested. [Work supported by NSF under Grant ECS 81-19886.]
Textural feature extraction in seismic images
Authors: Stephanou H. E. , Lu S. Y.
Published: October 2005

This lecture introduces a set of second-order statistical features that can be used to discriminate among several textural classes associated with seismic reflection configuration patterns. It is well known in the petroleum geology community that some of these patterns are characteristic of certain types of rock formations. The textural features that we use here are based on an extension of the co-occurrence matrix approach originally proposed by Haralick et al., in 1973. The feature extraction technique has been applied to a seismic image from offshore West Africa. The results indicate that the method is useful for the local discrimination of rock types deposited during the same geological period. Considerably more elaborate scene analysis techniques are however needed for image understanding purposes. They are not discussed in this talk.
Acoustic emission analysis using pattern recognition
Authors: Doctor P. G. , Daly D. S.
Published: October 2005

The purpose of the work is to design a method of differentiating events, caused by a growing crack in a critical structure from innocuous noise sources, from the waveform in order to improve the accuracy of acoustic emission monitoring systems for metal structures. The development approach is to generate acoustic emissions from known (crack, fretting, electrical transient) sources in the laboratory, compute certain quantities (features) from the recorded signal, and design discriminant functions to differentiate among the sources. The selection of the features for the discriminant function is crucial. They are selected on the basis of physical as well as empirical grounds. The acoustic signal is influenced by subtle environment effects as well as the instrument system, the geometry of the structure being monitored and its interaction with the changing geometry of the growing crack. The challenge of the work is finding features that are applicable to a range of monitoring situations and are reasonably stable over time. [Work supported by NRC Office of Nuclear Regulatory Research and Defense Advanced Research Project Agency.]
Speech recognition at IBM research
Authors: Jelinek Frederick
Published: October 2005

Continuous speech recognition is an attempt to develop a “voice-actuated typewriter” that automatically transcribes naturally spoken utterances into correct orthography. A reliable speech recognizer would facilitate the most economical speech compaction and transmission. The current IBM objective is to accomplish realtime transcription of office correspondence using an experimental system consisting of a minicomputer, several array processors, and an editing workstation with a display, keyboard, and printer. To make real-time performance possible, the vocabulary is restricted to 5000 words that must be spoken with short pauses between them. The lecture will describe the current state of the project, outline its methods, and discuss future prospects.
Pattern recognition in speech processing
Authors: Allen Jonathan
Published: October 2005

The determination of linguistic structure from surface patterns in text and speech requires the integration of cues from multiple constraint domains including phonetic features, syllable and morpheme structure, syntax, and semantics together with pragmatics. Utilization of these constraints shows that the factors contributing to the integration metric vary along the utterance, and that principled surface variation can be accounted for in terms of these structures, thus reducing the apparent noise. Given the large number of factors that influences the pattern classification decision, it is important to defer commitment to structural hypotheses as long as possible, so that neither “bottom up” nor “top down” search strategies are appropriate models for the recognition of natural language patterns. Instead, observance of cooccurrence relations among the parameters of a model can be exploited in efficient training procedures that extract the maximum amount of information from the experimental corpus. These techniques naturally lead to formulations of constraint domain structures that are mathematically explicit, minimizing the use of heuristics except where dictated by complexity considerations. Experience from contemporary research in speech synthesis and recognition is used to illustrate these principles, characterize current capability, and indicate directions for future research.
Propagation of axisymmetric free waves in a circular cylindrical shell
Authors: Trivett D. H.
Published: October 2005

This paper presents the results of an investigation of free wave propagation in a circular cylindrical shell in vacuum, using the linear theory of elasticity. The study has resulted in identifying a previously unreported low-phase velocity axisymmetric mode. This new mode is a low-frequency branch of the first mode in a cylindrical shell and exists below the cutoff frequency of the second axisymmetric mode. The physical properties of the two low-frequency branches are discussed and numerical results are presented along with preliminary data verifying the existence of the new mode. In addition, the results are used to demonstrate that present thin shell theory does not adequately describe the behavior of thin shells at low frequency.
Low-frequency vibrational modes of fluid-loaded thin spherical shells
Authors: Green L. H. , Hackman Roger H. , Trivett D. H. , Flax L.
Published: October 2005

The low-frequency form function for plane-wave scattering by a fluid-loaded thin spherical shell is characterized by the high Q monopole or “bubble” resonance. As the shell thickness is increased, the monopole resonance is observed to shift to higher frequency and broaden (i.e., the Q of the resonance decreases). With a further increase in thickness, high Q resonances appear on top of the spectrum of the monopole resonance. These low-frequency, high Q resonances, first reported by Diercks and Hickling [J. Acoust. Soc. Am. 41, 380–393 (1967)] have never been satisfactorily explained. In this paper we present the results of our investigation, based upon the linear theory of elasticity, of these high Q resonances. The dependence of the resonances on frequency, and shell and fluid parameters are presented along with the elastic stresses and displacements in the shell. Dispersion curves are generated from numerical solutions and a physical explanation for the strong coupling to the fluid medium is obtained.
Acoustic surface wave measurements on live bottlenose dolphins
Authors: Madigosky W. M. , Lee G. F. , Borkat F. , Kataoka R. , Haun J.
Published: October 2005

Measurements of the velocity and attenuation of acoustic surface waves propagating on the outer surface of live bottlenose dolphins (Tursiops truncatus) were made as a function of frequency and location on four different animals. Two miniature accelerometers were attached to the skin and a surface wave was launched using an electromagnetic shaker driven by a noise source. A dual channel FFT spectrum analyzer and computer analyzed and computed the data [see J. Acoust. Soc. Am. 73, 1374 (1983)]. Surface wave velocities varied from 4 to 14 m/s over the frequency range 100–1000 Hz. The attenuation appeared to follow the α = Af1.0 law, where, A ≃ 1.5 dB-s/m. Generally, the wave speed and attenuation were independent of the propagation direction (anterior, posterior, dorsal, or ventral) except near the dorsal fin. Additional measurements of the shear wave velocity were obtained on just the epidermis plus dermis section of the skin. These velocities were found to be two or three times higher and dependent on the direction of the propagation.
Transient Rayleigh wave transmission across periodic surfaces
Authors: Chamuel Jacques R. , Brooke Gary H.
Published: October 2005

Sharp attenuation of 10-Hz Scholte wave components has been observed in a region of the Canadian Arctic. The presence of shallow nearly periodic bottom ridges and surface features is believed to be the cause of the sharp attenuation of these low-frequency components (G. H. Brooke). Experimental investigations using ultrasonic models (Chamuel) have been carried out to study the transmission of transient Rayleigh waves across periodic surface grooves. Attenuation, dispersion, and time delay effects have been measured and related to groove dimensions and spatial distribution. The energy of the first Bragg frequency component is partly transmitted over a wide time window. Strong low-frequency components with a wavelength equal to 4 times the spatial wavelength of the grooves are transmitted. The effects of the number of grooves, and the groove depth and spacing on filtering and delaying the transmitted Rayleigh wave pulse will be described. The propagation of broadband transient Scholte waves across periodic surface grooves and ridges is being investigated. [Work sponsored by DREP.]
Measurements of periodic blade pressures on a transonic propeller with nonuniform inflow
Authors: Heidelberg Laurence J. , Dahl Milo D. , Rice Edward J.
Published: October 2005

As part of an experimental program to determine the installation effects on noise of a transonic propeller in front of a wing, blade surface pressures were measured. This paper is a preliminary investigation of these measurements with the purpose of relating pressure to blade angle of attack changes. The ultimate purpose is to use blade pressure as a tool to measure the inflow distortions and relate the resulting unsteady loading to noise. Several miniature pressure transducers were mounted on a highly swept transonic propeller known as SR-3. This propeller was run in a wind tunnel over a range of Mach numbers from 0.5 to 0.85. The propeller axis was set at several angles to the flow in order to produce a known inflow distortion. A second set of tests were run with a wing installed behind the propeller and the effect of this inflow distortion on blade pressures was measured. The magnitude of the pressure changes is shown as a function of the periodic angle of attack change. A significant phase lag between pressure and angle was noticed for transducers even near the leading edge of the blade.
Fan noise reduction achieved by removing tip flow irregularities behind the rotor
Authors: Dittmar James H. , Woodward Richard P. , MacKinnon Michael J.
Published: October 2005

One of the major noise producing mechanisms in a fan stage for a turbofan engine is the interaction of the rotor wakes with the downstream stator vanes. Previous work has indicated that the rotor tip flow irregularities (vortices and velocity defects) may be as large or larger a source of blade passage tone noise as the usually considered mean rotor wake. Flow was removed between the rotor and stator of an existing fan stage by an outer wall slot and noise measurements were made to investigate the rotor tip flow irregularity-stator interaction as a noise source. Farfield noise data taken in an inlet arc showed little tone noise reduction with flow removal, probably the result of rotor-stator interaction noise not propagating upstream through the rotor. In-duct measurements behind the fan stator did show noise reduction with flow removal and proportionally more reduction occurred with the first increment of flow removal than with subsequent amounts. Since the tip flow irregularities were assumedly removed with the first increment of flow, the duct measurements indicate that the tip flow irregularity-stator interaction is probably as large a noise producing mechanism as the normally considered rotor wake-stator interaction.
Surface aerosound from a model wing/flap in an anechoic room
Authors: Liu S.-C. , Meecham W. C.
Published: October 2005

The aerodynamic sound generated by a small scale wing model interacting with a 4-in. jet has been investigated experimentally in NASA-AMES anechoic chamber. The investigation consists of two parts. The first part is concentrated on the jet shear layer/wing interaction noise. The second part is the study of noise associated with separated flow. Cross-correlation techniques are used to discriminate against unwanted noise. The results of experiment 1 show that the sound generated by shear layer/wing interaction is 10 dB higher than the free jet noise. A round guide attached to the jet exit reduced the farfield sound by 8 dB. The rms pressure in the nearfield is found to be inversely proportional to the third power of the distance from generating eddies. The typical Strouhal number of sound generated, based on the shear layer thickness and the mean flow speed, is 0.17. The results of the sound experiment show that on the separation side of the wing the generating eddies are located near the trailing edge, as expected. The noise generating eddies propagate downstream with the convection velocity and are not triggered until they reached the trailing edge. The convection speed is found to be 0.85 times the jet mean flow speed, as judged by signal time delays.
Transillumination of the glottis during Hindi obstruents
Authors: Dixit R. Prakash , Baer Thomas , Honda Kiyoshi
Published: October 2005

The purpose of this study was to examine the degree of glottal opening and the temporal relationship between articulatory events and opening-closing gestures of the glottis during the production of Hindi obstruents which contain phonologically distinctive four manner categories of stops and affricates (voiceless unaspirated, voiceless aspirated, voiced unaspirated, and voiced aspirated) and two manner categories of fricatives (voiceless and voiced). To that end, we obtained glottograms, using transillumination technique, while a native speaker of Hindi produced disyllabic nonsense words of CVCVC form, where C was an obstruent and V was a high front unrounded vowel. All C positions in an individual word were occupied by the same obstruent. The vowel in the second syllable carried the stress. The glottograms, thus obtained, show a systematic relationship between articulatory events and opening-closing gestures of the glottis during various obstruents, which is fairly similar within the same category but quite dissimilar across different categories of obstruents. The degree opening also differs from one category of obstruents to another, however, within the same category of obstruents it is quite similar. The glottograms will be presented and discussed.
Kinematic studies of laryngeal articulation
Authors: Löfqvist Anders , McGarr Nancy S.
Published: October 2005

The present study was designed to contribute information on kinematic details of the glottal abduction-adduction gesture in voiceless consonant production. Transillumination was used to record glottal movements. The linguistic material consisted of multiple repetitions of dental stops and fricatives which differed in stress and were spoken at two different rates. Two native American English speakers served as subjects. As expected, glottal opening was larger for fricatives than for stops. Preliminary kinematic results suggest a stable positive relationship between maximum displacement and peak velocity of glottal movements. That is, peak velocity of both abduction and adduction was positively correlated with peak glottal opening for both fricatives and stops. An increase in glottal opening was also associated with stress, with stressed voiceless consonants having a larger peak glottal opening than their unstressed counter-parts. In general, peak velocity of glottal abduction was higher than that of glottal adduction. Results from laryngeal articulatory gestures are consistent with reports for other articulators. [Work supported by NINCDS and BRSG.]
Laryngeal adducation and tongue lowering movements in stop-consonant production
Authors: Munhall Kevin G. , Ostry David J.
Published: October 2005

Phonetic segments are instantiated across the vocal tract as a whole and the various articulators that shape the production mechanism thus co-determine segmental properties. This requires that the activity of the speech articulators be related in a systematic fashion. Perhaps the simplest manner in which different articulators could be coordinated is by sharing some kinematic characteristics. The present study examines the similarities between tongue dorsum lowering and vocal fold adduction during the production of the intervocal stop consonant in a CVCVC. Lexical stress was manipulated with either the first or second vowel receiving the primary stress. The movements of the two articulators were measured separately within a single session with a computerized ultrasound system. Preliminary analyses indicate a similarity in the form of adjustment to the stress manipulation across the two articulators. The time to reach peak velocity was shorter for both articulators in the post-stress context. Further, the movement onset times of the two articulators relative to oral implosion varied systematically with stress levels. The results are discussed in terms of inter-articulator timing.
Jet noise: An overview of the self and shear noise theory
Authors: Richarz W. G.
Published: October 2005

Lighthill's theory of aerodynamic sound furnishes an exact set of differential equations. In order to obtain reasonable estimates of sound generated by aerodynamic sources certain simplifications are introduced. One model that has been quite successful is Ribner's self and shear noise formalism. The equivalent source terms therein are proportional to the unsteady momentum flux directed at an observer. The theory has been extended to deal with forward flight affects, heated turbulent flows. In addition there are results for nearfield pressures as well as the farfield coherence. All this can be obtained without any alteration of the underlying formalism. The turbulent flow is described by a “locally homogeneous isotropic” correlation function with specified length and time scales. Despite its simplicity the model is capable of predicting many features of the sound field generated by subsonic jets. [Work supported by NSERC, Canada.]
Aircraft noise synthesis system: An introduction
Authors: McCurdy David A.
Published: October 2005

An aircraft noise synthesis system has been developed to provide test stimuli for studies of community response to aircraft flyover noise. The computer-based system generates realistic, time-varying audio simulations of aircraft flyover noise at a specified observer location on the ground. The synthesis takes into account the time-varying aircraft position relative to the observer; specified reference spectra consisting of broadband, narrow-band, and pure tone components; directivity patterns; Doppler shift; atmospheric effects and ground effects. These parameters can be specified and controlled in such a way as to generate stimuli in which certain noise characteristics such as duration or tonal content are independently varied while the remaining characteristics such as broadband content are held constant. The system can also generate simulations of the predicted noise characteristics of future aircraft such as the proposed advanced turboprop. The paper includes a brief description of the overall system, a user-oriented discussion of the input data and modeling methods, and recordings of synthesized flyover noise produced with the system.
Aircraft noise synthesis system: Computer algorithms and methods
Authors: Grandle Robert E.
Published: October 2005

This paper describes in some detail the algorithms and methods used in the aircraft noise synthesizer program now in use at the Aircraft Noise Reduction Laboratory. This program is intended to produce aircraftlike flyover noise from a series of pure tone, narrow-band, and third-octave spectrums. Because the acoustic output of this program is intended to be played to subjects for determination of the fundamental response of humans to aircraft noise, a great deal of care must be taken to reduce to a minimum any extraneous noise produced by the synthesis process. In general the method described in this paper makes use of the fast Fourier techniques to produce analog time histories from the narrow-band power spectrum which is its input. The basic problem of noise synthesis of nonperiodic noise with a semi-periodic component (turbine and compressor whine) is to produce a sound which is sufficiently random enough to sound natural while maintaining a tight control of the spectral levels. The major difficulty in this is that the input spectral levels lack sufficient information to produce a continuous analog time history.
Brainstem evoked responses to vibratory stimuli in terrestrial and marine turtles
Authors: Lenhardt M. L.
Published: October 2005

A startle to acoustic stimulation is a primitive indication of hearing in vertebrates. Turtles have not been shown to startle to airborne sounds but do exhibit this reflex when audio frequencies are applied directly to the shell. Evoked responses were recorded to airborne and vibratory clicks using needle electrodes. Both stimuli yielded similar waveforms, with the exception of a slight time delay due to propagation in bone. When equated for equal latencies the vibratory stimuli seemingly had a greater dynamic range. Simultaneous stimulation with white noise masking in the other modality further suggested preferential response of the ear to vibratory stimuli. Somatosensory input was controlled by anesthetic manipulation of the vertebral column at C1. The results indicate that the turtles are more sensitive to vibrations than airborne sound and bone conduction may be the preferred route to the ear.
The relation between the human frequency following response and the low pitch of complex tones
Authors: Chambers Ron D. , Feth Lawrence L. , Burns Edward M.
Published: October 2005

The objective of this study was to examine the relation between the value of the low pitch of complex tones and the f0 of the frequency following response (FFR). Mean pitch matches between a series of six-component complex tones and comparison pure tones were obtained for four normal hearing subjects with extensive musical training. FFRs were recorded in response to the complex stimuli which were most divergent in pitch for each subject and to pure tone signals of equal pitch. The FFR records were analyzed for frequency composition. The f0 of the FFRs elicited by complex tones did not covary with frequency or pitch shift; the fundamental remained much closer to 200 Hz (the frequency with the period of the stimulus waveform). The f0 of the FFR to pure tones with pitch equal to the complex tones also approximated the stimulus waveform. It was suggested that the output of the neural mechanisms reflected in the FFR does not vary in a manner consistent with shift in low pitch of complex stimuli. [Work supported by NIH.]
Asymmetries in pitch perception of dichotic chords and middle latency evoked potentials
Authors: Hood L. J. , Berlin C. I. , Baker D. J.
Published: October 2005

The dominance of one ear over the other in the perception of pitch of dichotic chords has been reported by Efron and Yund [J. Acoust. Soc. Am. 59, 889–898 (1976)] and in subsequent studies by that group. The present investigation addressed the existence of correlations between psychophysical and electrophysiological asymmetries. Specifically, the relation between ear dominance measured psychophysically using the Efron paradigm and right-left asymmetries in middle latency auditory evoked potentials was examined in ten normal-hearing adult subjects. Absolute and interwave latencies were obtained for middle latency responses to right and left monaural, binaural, and dichotic presentation conditions using tonal stimuli. Rank order correlation coefficients were used to compare right-left ear and hemifield evoked potential latency differences to measures of ear dominance. Results indicated that latency measures, particularly for components involving wave Pb of the middle latency response, correlated with the direction of ear dominance. The characteristics of these correlations will be discussed. [Supported by NINCDS ♯NS 11647, the Louisiana Lions Eye Foundation, and the Eye and Ear Foundation.]