摘要:

Abstract not available.

ISSN:0001-4966    

DOI:10.1121/1.423891

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

The purpose of these acoustical patent reviews is to provide enough information for a Journal reader to decide whether to seek more information from the patent itself. Any opinions expressed here are those of the reviewers as individuals and are not legal opinions. Printed copies of United States Patents may be ordered at $3.00 each from the Commissioner of Patents and Trademarks, Washington, DC 20231. Patents are available via the Internet athttp://www.uspto.gov.

ISSN:0001-4966    

DOI:10.1121/1.423783

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

Pool boiling experiments from a platinum wire heater in FC-72 liquid were conducted under terrestrial and microgravity conditions, both with and without the presence of a high-intensity acoustic standing wave within the fluid. The purpose of this research was to study the interaction between an acoustic field and a pool boiling system in normal gravity and microgravity. The absence of buoyancy in microgravity complicates the process of boiling. The acoustic force on a vapor bubble generated from a heated wire in a standing wave was shown to be able to play the role of buoyancy in microgravity. The microgravity environment was achieved with 0.6 and 2.1-s drop towers. The sound was transmitted through the fluid medium by means of a half wavelength sonic transducer driven at 10.18 kHz. At high enough acoustic pressure amplitudes cavitation and streaming began playing an important role in vapor bubble dynamics and heat transfer. Several different fixed heat fluxes were chosen for the microgravity experiment and the effects of acoustics on the surface temperature of the heater were recorded and the vapor bubble movement was filmed. Video images of the pool boiling processes and heat transfer data are presented.

ISSN:0001-4966    

DOI:10.1121/1.423910

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

It is widely assumed that the proper transformation of acoustic amplitude to electric amplitude is a critical factor affecting speech recognition in cochlear implant users. The goal of this study was to investigate the effects of instantaneous nonlinear amplitude mapping on vowel and consonant recognition in both cochlear implant users and normal-hearing listeners. A four-channel noise-band speech processor was implemented, reducing spectral information to four bands. A power-law transformation was applied to the amplitude mapping stage in the speech processor design, and the exponent of the power function varied from a strongly compressive(p=0.05)to a weakly compressive value(p=0.75)for implant listeners and from 0.3 to 3.0 for acoustic listeners. Results for implants showed that best performance was achieved with an exponent of about 0.2, and performance gradually deteriorated when either more compressive or less compressive exponents were applied. The loudness growth functions of the four activated electrodes in each subject were measured and those data were well fit by a power function with a mean exponent of 2.72. The results indicated that best performance was achieved when the normal loudness growth was restored. For acoustic listeners, results were similar to those observed with cochlear implant listeners, except that best performance was achieved with no amplitude nonlinearity(p=1.0).The similarity of results in both acoustic and electric stimulation indicated that the performance deterioration observed for extreme nonlinearity was due to similar perceptual effects. The function relating amplitude mapping exponent and performance was relatively flat, indicating that phoneme recognition was only mildly affected by amplitude nonlinearity.

ISSN:0001-4966    

DOI:10.1121/1.423912

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

Rigorous formalisms are presented for the numerical solution of problems of acoustic scattering by bounded obstacles in three dimensions. These methods are based on a perturbative technique recently demonstrated in problems of diffraction by gratings. Like those grating solvers, these new bounded-obstacle algorithms can produce highly accurate solutions for a wide variety of scattering geometries.

ISSN:0001-4966    

DOI:10.1121/1.423840

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

A spring model for the simulation of the propagation of ultrasonic pulses in arbitrarily complex heterogeneous media is proposed in the framework of the local interaction simulation approach (LISA). The algorithm used allows us to include heuristically additional local interaction mechanisms. In particular, the problem of propagation of pulses across imperfect contact interfaces is considered. A contact quality tensor, which is expected to be connected, although not necessarily in a trivial way, to the bond quality, is introduced directly into the model in order to treat interface flaws, such as delaminations and/or slipping bonds. To demonstrate the applicability of the technique, which is particularly suitable for parallel processing, a few examples of numerical simulation of pulse propagation in media with various kinds of imperfections are presented.

ISSN:0001-4966    

DOI:10.1121/1.423841

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

The propagation of high-frequency linear waves in a smoothly inhomogeneous isotropic elastic medium is considered. The dilatation of theSwave is found via employment of both the zeroth- and first-order terms of the elastic field by a ray analysis. It is observed that the dilatation is necessarily dependent upon the inhomogeneity of the medium, vanishing in the instance the medium is taken homogeneous.

ISSN:0001-4966    

DOI:10.1121/1.423842

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

The high-frequency propagation of acoustic plane waves in a weakly heterogeneous random stationary 2-D medium is considered. The apparent velocity of the wave is larger than the velocity corresponding to the background homogeneous medium; the difference is called velocity shift. Both this shift and the variance of the apparent velocity are calculated using the Rytov approximation; explicit formulas are given when the covariance of the medium is Gaussian. This enables one to show several properties of the shift and the variance, which are illustrated by some numerical experiments on the wave equation.

ISSN:0001-4966    

DOI:10.1121/1.423843

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

This paper deals with the elastodynamic finite integration technique for axisymmetric wave propagation in a homogeneous and heterogeneous cylindrical medium (CEFIT). This special variant of a finite difference time domain (FDTD) scheme offers a suitable method to calculate real three-dimensional problems in a two-dimensional staggered grid. In order to test the accuracy of the numerical CEFIT code, problems for which analytical solutions are available are presented. These solutions involve wave propagation in an elastic plate, the scattering of a plane longitudinal wave by a spherical obstacle, and ultrasound generation by a thermoelastic laser source. For the latter problem experimental results are included. The CEFIT code also allows the treatment of more complicated problems. Further possible applications are the investigation of elastic waves generated in an acoustic microscope, the simulation of impact-echo measurements in multi-layer systems, axisymmetric wave propagation in arbitrary bodies of revolution, the calculation of elastic wave fields of longitudinal wave transducers with a circular aperture, and the investigation of multi-layer models for particulates.

ISSN:0001-4966    

DOI:10.1121/1.423844

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

Results are reported for direct and inverse scattering of plane acoustic waves from sound-hard scatterers of arbitrary shapes in an infinite, homogeneous ambience. The direct problem is solved via a shape deformation technique which is valid for finite deformations. The resulting solution requires solving only a set of algebraic recursion relations, but neither integral equations nor Green’s function. The methodology has three essential features: all calculations refer exclusively to a known simple boundaryΓsinstead of the iteratively updated scatterer shapes; the Jacobian of the scattered field is evaluated by solving a series of Helmholtz’s equations (with different boundary data) in the region exterior to the simple shapeΓs;and no ambiguity in the solution arises due to the interior eigenvalues. The inverse problem of recovering the scatterer boundary shape is solved by least square minimization using the Levenberg–Marquardt algorithm. Inversions of several two-dimensional shapes with varying degrees of complexity are reported. The procedures described generalize straightforwardly to transmission and three-dimensional problems.

ISSN:0001-4966    

DOI:10.1121/1.423845

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP