摘要:

Abstract not available.

ISSN:0001-4966    

DOI:10.1121/1.418298

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

Abstract not available.

ISSN:0001-4966    

DOI:10.1121/1.418378

出版商:Acoustical Society of America    

年代:1997

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:10.1121/1.418277

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

This work provides theoretical and empirical arguments in favor of an approach to phonetics that is called double-weak. It is so called because it assumes relatively weak constraints both on the articulatory gestures and on the auditory patterns that map phonological elements. This approach views speech production and perception as distinct but cooperative systems. Like the motor theory of speech perception, double-weak theory accepts that phonological units are modified by context in ways that are important to perception. It further agrees that many aspects of such context dependency have their origin in natural articulatory processes. However, double-weak theory sides with proponents of auditory theories of phonetics by accepting that the real-time objects of perception are well-defined auditory patterns. Because speakers find ways to obey “orderly output conditions” (Sussman et al., 1995), listeners are able to successfully decode speech using relatively simple pattern-recognition mechanisms. It is suggested that this situation has arisen through a stylization of gestural patterns to accommodate real-time limits of the perceptual system. Results from a new perceptual experiment, involving a four-dimensional stimulus continuum and a 10-category /hVC/ response set, are shown to be largely compatible with this framework.

ISSN:0001-4966    

DOI:10.1121/1.418290

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

A new impulse inverse formula and it’s generalization including arbitrary input, are proposed. The new generalized inverse formula has the advantage of not being necessary to specify the first digital value of the input. Numerical instability of the inverse formula for arbitrary input is investigated carefully. An analysis of the perturbed stability and Lyapunov exponent are carried out. As the result of this analysis, it is shown that the estimated error is sensitive to the experimental error and previously estimated error as a sequential algorithm. Simulation using experimental data is also shown in the paper.

ISSN:0001-4966    

DOI:10.1121/1.418341

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

The scattering of antisymmetric flexural waves is illustrated via three series of experiments conducted on linear elastic solid wedges immersed in air. It is quantitatively demonstrated that scattering into different modes exists when an antisymmetric mode is reflected at the end face of a wedge or when it is submitted to an external pressure applied on the tip of the wedge. The existence of transmission of edge modes is also experimentally confirmed.

ISSN:0001-4966    

DOI:10.1121/1.418342

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

A generalized internal source density (GISD) method is presented to address the forward and backward projection of harmonic pressure fields from complex three-dimensional bodies. The GISD approach is based on decomposing the field on a closed surface of revolution in the fluid into a summation of circumferential orders where the pressure field for each order is associated with an internal linear distribution of ring sources on the axis of revolution of the surface. Both Dirichlet and Neumann boundary value problems may be addressed using the approach in which the axial variation of each ring source distribution is formulated as the solution of a minimum mean square error problem which is subsequently solved using SVD methods. The resulting linear distributions of ring sources can be simply used to determine the entire pressure and velocity fields of a complex harmonically vibrating body. In particular, the pressure and/or normal velocity on a vibrating body can be readily obtained from the pressure field over a closed surface. Local intensity and radiated power can thus be simply obtained. Far field pressures are simply obtained from the axial Fourier transforms of the ring source distributions. Several examples are presented to illustrate the behaviour of the source distributions for spherical geometries. The analytical results obtained via the GISD method agree with those obtained via classical methods.

ISSN:0001-4966    

DOI:10.1121/1.418343

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

Coplanar arrays of small longitudinal ultrasonic transducers acquire a set of waveforms which are initially plotted as an amplitude image in the offset-time domain. This amplitude image is then mapped to the intercept time-horizontal slowness(τ−p)domain via a slant-stack Radon transformation. The shape of the locus of these arrivals inτ−pspace directly provides information on the propagation angle-dependent phase velocities in an anisotropic medium. The method is applied to an isotropic acrylic and an anisotropic laminate with orthorhombic symmetry. The method allows determination of the phase velocities over an 80° range of propagation angles. The acrylic is isotropic with a phase velocity of 2780 m/s which differs little from that determined in a conventional pulse transmission. The phase velocities versus propagation angle were measured in three planes of symmetry and in one off-symmetry plane in the laminate. Anisotropies of up to 22% over an 80° range of propagation angles were found in the planes perpendicular to the layering. The plane containing the layering was only weakly anisotropic with velocities dependent on the weave of the fiber mats.

ISSN:0001-4966    

DOI:10.1121/1.418344

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

In this paper, the finite element method (FEM) is used to solve the three-dimensional poroelasticity problem in acoustics based on the isotropic Biot–Allard theory. A displacement finite element model is derived using the Lagrangian approach together with an analogy with solid elements. From this model, it is seen that the “damping” and “stiffness” matrices of the poroelastic media are complex and frequency dependent. This leads to cumbersome calculations for large finite element models and spectral analyses. To overcome this difficulty, an efficient algorithm is proposed. It is based on low-frequency approximations of the frequency-dependent dissipation mechanisms in poroelastic media. This efficient algorithm allows the poroelastic materials to be modeled with classical FEM codes. Also, the acoustic–poroelastic and the poroelastic–poroelastic coupling conditions are presented. The proposed model is compared to existing literature for both two-dimensional and three-dimensional problems. Excellent comparisons prove both the accuracy and effectiveness of the proposed model and its coupling with acoustic elements. Finally, to show the usefulness of the proposed model, the edge effect on the absorption coefficient of a multilayered poroelastic material is presented. Results show that both analytical models based on laterally infinite poroelastic layers, and standing wave tube measurements may be misleading at low frequencies.

ISSN:0001-4966    

DOI:10.1121/1.418345

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

This paper presents a theoretical study of the acoustic dispersion in media containing many spherical scatterers. The existing dispersion relation is used to investigate the dispersion in media containing particles such as low acoustic-contrast fluid, rigid and elastic spheres, as well as air bubbles. It is shown that in the case of low acoustic-contrast fluid, rigid and elastic spheres, the presence of scatterers has more profound effects on the acoustic attenuation than on the phase speed, whereas in the bubble case, both the attenuation and phase speed can be affected significantly. Then the dispersion relation is examined via the Kramers–Kronig relations, as they express a general identity for dispersion and are therefore ideal to test the suitability of a specific model for acoustic propagation. Results indicate that although there remain some discrepancies, the existing dispersion relation satisfies the Kramers–Kronig relations reasonably well. Good agreement is particularly apparent in the bubble case. Possible cause for the discrepancies is also discussed in connection with a discussion of the assumptions that lead to the dispersion relation.

ISSN:0001-4966    

DOI:10.1121/1.418311

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP