摘要:

In the auditory cortex of anesthetized cats, single neurons were studied for their sensitivity to tones presented against backgrounds of continuous wide‐spectrum noise. Tone pulses and noise stimuli were mixed acoustically and presented using calibrated, sealed stimulating systems. Data collected were spike‐rate intensity functions for tones delivered alone and in the presence of noise. In most neurons, noise of any given intensity induced tone sensitivity shifts that were greatest for frequencies to which the neurons were most sensitive. When the sensitivity loss was in excess of about 15 dB, continuous noise usually caused a steepening of the slope of the tone intensity function. These data suggest that the excitatory response area of a cortical neuron is shaped by multiple, incompletely overlapping inputs of varying sensitivities. In the presence of a continuous noise mask, the disparate thresholds of these inputs may be brought into closer register, resulting in a steepened rate intensity function. These observations may be germane to the neural genesis of the ‘‘recruitment’’ seen in the loudness judgments of normal listeners for masked tones.

ISSN:0001-4966    

DOI:10.1121/1.394178

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

This paper introduces two recursive realizations of the phase transform (PHAT) processor for time‐delay estimation (TDE), using a simple one‐pole low‐pass filter and the least‐mean‐square (LMS) adaptive filter, respectively. It is shown that these adaptive methods are capable of tracking time‐varying delay functions which correspond to moving sources or receivers, and are very effective in reducing the effect of interfering tonals which must be generated by the target as jamming signals to mask its movement. The performances of these methods are compared with those of other existing adaptive TDE algorithms via computer simulations.

ISSN:0001-4966    

DOI:10.1121/1.394161

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

This paper introduces the formulation of the optimal image reconstruction algorithm for finite‐size objects. For practical data acquisition and computation considerations, the partial discrete (continuous–discrete) model is used for the formulation. The basic constraints utilized in this optimization process are the finite size of the object and the limited spatial‐frequency bandwidth of the resultant wave field. The result indicates that the algorithm consists of a linear matrix transformation followed by backward propagation. It is also shown that the bandlimited wave field extrapolation method and backward propagation technique are degenerate cases of this optimal algorithm. In addition to image reconstruction, the formulation of this optimal algorithm can be used to determine the optimal wave field sampling for efficient data acquisition.

ISSN:0001-4966    

DOI:10.1121/1.394461

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

Details of a procedure for efficiently and accurately calculating various auditorium acoustics measures from pistol shots are described. Early/late sound ratios, decay times, center time, and modulation transfer functions are calculated in octave bands. Measurements for a wide range of acoustical conditions are compared with simple predictions, and various quantities are found to be strongly intercorrelated.

ISSN:0001-4966    

DOI:10.1121/1.394162

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

Measurements of sound transmission loss made using nine different methods to estimate the effects of room absorption are reported. A single wall specimen was used in five different positions in the opening of a laboratory sound transmission loss test suite. Four different levels of room absorption were used. The conventional decay method is shown to work well in all cases, as does a method using a sound source with a known power to estimate the room absorption. A method using a sound‐pressure level near the source and the room average, the near–far method, did not work as well.

ISSN:0001-4966    

DOI:10.1121/1.394165

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

The diffraction of a Gaussian ultrasonic beam in absorbing fluids produces a Gaussian field distribution in the fundamental component. An analytical expression for the second harmonic is derived and it is also a Gaussian function in the quasilinear approximation. Our expressions for the second harmonic are free of the nearfield oscillations characteristic of the radiation from a piston transducer. Calculated results are compared with measurements taken with a Gaussian transducer. Reasonable agreement between theory and experiment is found for both the fundamental and the second harmonic of an initially sinusoidal Gaussian ultrasonic beam in water at 2 MHz. An Appendix is given in which expressions are derived for the first four harmonics of a Gaussian beam. All harmonics are found to obey a Gaussian function. Moreover, the Gaussian coefficient of thenth harmonic is exactlyntimes that of the fundamental component. This means that the width at half maximum changes in proportion to 1/(n)1/2. The phase shift across the beam behaves in a similar manner.

ISSN:0001-4966    

DOI:10.1121/1.394166

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

Similar to the resonant‐sphere method in its experimental aspect, a resonant‐cylinder technique is developed for the measurement of the internal friction of solids. The solutions of the theoretical problems of using the cylinder instead of sphere are presented: the computation of the resonance spectrum of the cylinder (axially symmetric modes only); the evaluation of theQfactor from the experimental resonance spectrum, characterized by a low (peak/background) ratio; and the separation of the dilatational and shear oscillation components in the total value of internal friction, measured for a given resonance mode. The anisotropy of viscoelastic parameters in a rolled bar of commercial steel has been measured as a method sensitivity check. Other preliminary experimental data are also presented as illustrative examples.

ISSN:0001-4966    

DOI:10.1121/1.394167

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

Magnetothermoelastic axial wave propagation for soft ferromagnetic materials is discussed, both analytically and numerically. Assuming that a constant magnetic field is applied along the axial direction, the frequency equation is obtained for linear thermal radiation and traction‐free boundary conditions.

ISSN:0001-4966    

DOI:10.1121/1.394168

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

An apparatus and method of experimentation for measuring frequency‐dependent angle scattering frominvitrotissue samples and tissue‐like scattering media have been developed. Distinguishing features of this method are that data collection is rapid, data reduction is simple, and results, given in the form of the differential scattering cross section per unit volume, are accurate and absolute. Reported are the results of tests to determine the overall accuracy of the method. Also, results of the differential scattering cross section per unit volume from female human breast tissue are presented.

ISSN:0001-4966    

DOI:10.1121/1.394169

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

The normal‐mode solution to the problem of acoustic wave propagation in an isovelocity ocean with a wavy surface is considered. The surface wave amplitude is assumed to be small compared to the acoustic wavelength, and the method of multiple scales is employed to study the interaction between normal‐mode acoustic waves and the surface waves. A nonresonant interaction causes small fluctuations of the amplitude and phase of the acoustic wave at a rate dependent on the frequency of the surface wave. Backscatter occurs if the wavenumber of the surface wave is larger than that of the acoustic wave. The interaction becomes resonant if appropriate phase‐matching conditions are satisfied. In this case, two acoustic normal modes get coupled, resulting in a large‐scale periodic exchange of energy from one mode to another.

ISSN:0001-4966    

DOI:10.1121/1.394179

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP