摘要:

We reported that ionic permeability changes in the endolymph‐perilymph barrier contribute a significant factor in the physiological mechanisms underlying the noise‐induced hearing loss (J. Acoust. Soc. Am.64, S132 (1978)]. An indirect method of estimating permeability changes is to measure alterations of electrochemical potentials during anoxia, from which the contribution of passive ion movement can be calculated. This allows differences of permeability of the endolymph‐perilymph barrier between normal and noise exposed guinea pigs to be indirectly assessed. The endocochlear potential (EP) andK+concentrations of endolymph and perilymph were simultaneously measured in the basal turn of the guinea pig cochlea with a pair of double barreledK+selective electrodes. When anoxia was induced in guinea pigs treated with dihydrostreptomycin, the rate of decline of both EP and chemical potential forK+was reduced compared with normal animals. In guinea pig exposed to broad band noise at 115 dBAfor periods ranging from 3 to 17 days, initial results indicate that the decline of the electrochemical potential is reduced but not to the extent found in dihydrostreptomycin treated animals. Results of analysis on electrochemical potential changes in noise exposed guinea pig cochlea during anoxia will be presented.

ISSN:0001-4966    

DOI:10.1121/1.2017049

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

Tone‐on‐tone masking and differential electrode techniques have been employed to investigate the tuning properties of the DIF summating potential (SP). In these experiments the SP is elicited by tone bursts of set frequency and intensity while a second tone of variable frequency and level is used to reduce SP magnitude to a desired degree. The SP tuning curve is generated by frequency—intensity pairs formed by the masker that yield a preset decrease. Results reveal that DIF and whole nerve action potential (WNAP) tuning curves are quite similar while tuning properties of the DIF+are more analagous to CM interference functions. The dependence of various features of these SP tuning curves upon stimulus frequency and level are detailed in the present work. [Work supported by NINCDS.]

ISSN:0001-4966    

DOI:10.1121/1.2017105

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

There are several experiments involving single‐cell recording which are clearly measuring peripheral processes only (i.e., do not involve efferent action): steady‐state rate functions versus amplitude, click response PST histograms, sine‐wave tuning curves, envelope response to brief noise and tone pulses, steady‐state two‐tone inhibition, envelope response to steady tone plus inhibiting tone pulse, and transient response to closely spaced click pairs. Ideally, one would like to construct a model of the mechanical to neural transduction process which encompasses all of the above results. Several models have appeared in the literature over the past 15 years, but each matches only a limited set of experiments. However, we have combined the most promising features of several of these models to synthesize a new model which at least qualitatively matches all of the experimental data listed above except the click‐pair experiments, and has some physiological validity. Detailed comparisons between experimental data and computer generated simulations will be presented. [Supported by Defense and Civil Institute of Environmental Medicine.]

ISSN:0001-4966    

DOI:10.1121/1.2017123

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

In a letter to the editor, Barash [J. Acoust. Soc. Am.43, 378–380 (1968)] presented experimental evidence of the fact that for a divergent wave in a refractive medium caustics and turning points are clearly separated and phase shifts occur at the caustics only. In a rebuttal, Tolstoy [J. Acoust. Soc. Am.43, 380–381 (1968)] implied that while Barash's evidence was interesting, the accompanying conclusions lacked generality. In another letter, Silbiger [J. Acoust. Soc. Am.44, 653–654 (1968)] illustrated that there was theoretical evidence for Barash's conclusions by deriving an asymptotic short‐wave length solution to the wave equation appropriate to a point source in a vertically stratified medium by means of the WKBJ method. In this paper it is demonstrated that for a purely refracted ray emanating from a point source in a vertically stratified medium which possesses a single sound‐speed minimum, (1) the ray first encounters a caustic after its first turning point and before its second, (2) the ray encounters only one caustic between turning points, and (3) for that ray, turning points and points of encounter with caustics approach one another with increasing range from the source. These conclusions are in agreement with those of Silbiger, but are arrived at through rigorous geometrical acoustic means. [Work supported by AFGL.]

ISSN:0001-4966    

DOI:10.1121/1.2017127

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

The plane‐wave reflection coefficient for a continuously stratified fluid sediment can be simply calculated by representing the sediment as a stack of thin homogeneous layers. The error in such an approximation is usually estimated by increasing the number of layers and comparing the result with the original calculation. This kind of iterative approach can be both time consuming and frustrating. In this paper, the distorted‐wave Born approximation (DWBA) is used to derive a formula for the error associated with a single thin layer (local error) as well as for the total or global error. The local error formula can be used to devise a reasonablea priorilayering scheme for any continuous fluid sediment. The global error formula then allows an accurate estimate of the total error to be calculated at the same time as the reflection coefficient. Numerical results are presented for the case where the square of the wave number varies linearly with depth. The DWBA formula is shown to give an excellent estimate of the actual global error. [Work supported by Naval Electronic Systems Command.]

ISSN:0001-4966    

DOI:10.1121/1.2017132

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

It has recently been determined that the East Australian Current swings away from the Australian coast at 32° south latitude flows east across the Tasman Sea past the northern tip of New Zealand. As a result this large current may have a significant effect on sound propagation conditions near the north island of New Zealand. Sound propagation predictions are obtained using a multi profile modelling program. First, comparison is made between sound crossing the current and sound propagation in a normal subtropical water mass. The relative importance of thermal structure, bottom slope and bottom absorption are then determined for current flow near the continental shelf and bathymetric features such as the Lord Howe Rise and Three Kings Islands. Finally, results are compared to data obtained during Project Span Three.

ISSN:0001-4966    

DOI:10.1121/1.2017139

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

The attenuation of the first acoustic normal mode was measured for sound propagation in shallow water off the coast of Daytona Beach, Florida. The use of small explosive charges as a source permitted mode attenuation measurements over a frequency range extending from 40 to 800 Hz. Isolation of the first mode was accomplished by selecting source and receiver depths to minimize excitation and reception of the second and third acoustic normal modes. Higher order modes decayed rapidly with range and hence constituted a negligible contribution to the received pressure field. The results obtained from short range measurements are compared with long range propagation loss. [Work supported by the Naval Sea Systems Command.]

ISSN:0001-4966    

DOI:10.1121/1.2017144

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

Waves in linearly elastic media of infinite extent, composed of alternating layers of two different materials with perfectly bonded interfaces, exhibit some special features which are due to periodicity and impedance discontinuities at each interface. Floquet's theory permits an analysis of such waves which naturally separates into problems of anti‐plane and plane strain. The recently developed dispersion relations for such waves will be discussed, placing emphasis on the special features, such as existence of stopping bands, transition points, conical points, and asymptotic behavior. More. recent work on the applicability of Floquet‐type solutions in anti‐plane strain to layered semi‐infinite media with traction‐free surfaces parallel to the layers and to layered plates will also be discussed. A new class of surface is shown to exist which are dispersive, are restricted to a limited frequency range in some cases, and which can be propagating or evanescent. Finally. attempts to mathematically, model waves in periodically layered media by means of approximate theories will be mentioned, in particular the class of “effective dispersion” theories, which contain both the dispersive and the filtering properties.

ISSN:0001-4966    

DOI:10.1121/1.2017146

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

Recent experimental investigations by M. A. Breazeale, L. Adler, and G. W. Scott [J. Appl. Phys.48, 530–537 1977)] have verified the theory of Bertoni and Tamir [Appl. Phys.2, 157–172 (1973)]. Excitation of leaky Rayleigh waves takes place at the liquid‐solid interface when a Gaussian ultrasonic beam is incident at or near the Rayleigh angle to the interface. Now we should like to report two additional examples of leaky wave generation: (1) When a thin (less than a wavelength) ceramic layer is added to a metal surface, leaky waves are generated. The velocity and amplitude distribution of these waves will be discussed. (2) For interfaces such as water‐Plexiglas no real solution of the leaky Rayleigh velocity exists since the sound velocity in the water is larger than the shear velocity in Plexiglas. By studying the reflection of an incident Gaussian beam from water‐Plexiglas interfaces we have observed leaky waves near the longitudinal critical angle. Similar observations were made at water‐sediment interfaces. [M. A. Breazeale and L. Bjørnø, Proc. Ultrasonics Int., 1977, pp. 440–444]. [Research supported in part by the Office of Naval Research.]

ISSN:0001-4966    

DOI:10.1121/1.2017148

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

We discuss the problem of determining the minimum reflectance achievable with a given inhomogeneous layer thickness, substrate input impedance and range of allowed material parameters for normally incident, monochromatic sound waves. The density and dilitation modulus are permitted to vary independently. Real and complex moduli are considered. In the case of real parameters, analytic solutions for the switching curves and sublayer thicknesses of the multilayer system are presented. The resulting sublayer sequences will be discussed. The sequences are periodic and we show that for certain combinations of parameters the reduced unit cell thickness is approximately equal to 2π radians. General results concerning the parametrization of sublayers in the case of complex moduli will be discussed. Examples of particular solutions will be presented.

ISSN:0001-4966    

DOI:10.1121/1.2017154

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP