摘要:

Abstract not available.

ISSN:0001-4966    

DOI:10.1121/1.423101

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

Abstract not available.

ISSN:0001-4966    

DOI:10.1121/1.422994

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.423096

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:10.1121/1.422995

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

The precedence effect (PE) is a perceptual phenomenon that reflects listeners’ ability to suppress echoes in reverberant environments. The PE is not present at birth and appears only several months postnatal. Recent physiological studies have demonstrated correlates of the PE in the central nucleus of the inferior colliculus (ICC) of adult animals. The present study extended the same techniques to search for similar correlates in the ICC of kittens during the first postnatal month. Stimuli consisted of pairs of clicks or noise bursts presented from different locations in free field or with different inter-aural differences in time (ITD) under headphones, with an inter-stimulus-delay (ISD) between their onsets. Results suggest that a physiological correlate of the PE, i.e. suppression of responses to the second source, is present as early as 8 days postnatal, and occurs at similar ISDs to those recorded in adult cats. Suppression in kitten neurons varies with stimulus level, duration, and azimuthal position, in a similar manner to that in adult neurons. The age at which correlates of the PE in the kitten can be found precedes the age at which kittens can localize sound sources effectively, and presumably before the age at which they would demonstrate the PE behaviorally. Thus, the neural mechanisms that might be involved in the first stages of processing PE stimuli may be in place well before the behavioral correlate develops.

ISSN:0001-4966    

DOI:10.1121/1.423072

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

Recent studies have shown that when phonating subjects hear their voice pitch feedback shift upward or downward, they respond with a change in voice fundamental frequency(F0)output. Three experiments were performed to improve our understanding of this response and to explore the effects of different stimulus variables on voiceF0responses to pitch-shift stimuli. In experiment 1, it was found that neither the absolute level of feedback intensity nor the presence of pink masking noise significantly affect magnitude or latency of the voiceF0response. In experiment 2, changes in stimulus magnitude led to no systematic differences in response magnitudes or latencies. However, as stimulus magnitude was increased from 25 to 300 cents, the proportion of responses that changed in the direction opposite that of the stimulus (“opposing” response) decreased. A corresponding increase was observed in the proportion of same direction responses (“following” response). In experiment 3, increases in pitch-shift stimulus durations from 20 to 100 ms led to no differences in theF0response. Durations between 100 and 500 ms led to longer duration voiceF0responses with greater response magnitude, and suggested the existence of a secondF0response with a longer latency than the first.

ISSN:0001-4966    

DOI:10.1121/1.423073

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

Many geophysical applications of the array sonic measurements require the knowledge of the true source-time function. Recovery of the source-time function from the borehole sonic P head waves is different from the source inversion problem in exploration seismology. The difficulty in the inversion of borehole sonic measurements arises due to the inexact knowledge of the impulse response, e.g., the inability to model the whole problem including the tool body and transducers. The random noise often encountered in seismic signals is not the key obstacle here. The inverse source problem is ill posed due to the interference of P head-wave multiples. Using waveforms from a laboratory scale model we have applied two deconvolution methods, one using a Wiener filter and the other the time-domain least-squares method. As expected, without constraints on the solutions, one cannot recover a satisfactory source-time function. An unconventional smoothness constraint is applied in the source spectrum (instead of the usual smoothness in the time-domain signals), which corresponds to a finite-duration pulse in the time domain (instead of the usual band-limited spectrum). This technique is thus called the “duration-limited” inversion. The inverted results, obtained by Wiener filtering combined with this “duration limiting” process and multichannel stacking, agree well with an independent free-field measurement. Furthermore, reconstructed receiver waveforms using the inverted source function match the measured ones. The inversion procedure is robust and potentially useful for field measurements.

ISSN:0001-4966    

DOI:10.1121/1.423074

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

A procedure for the measurement of intrinsic scattering object properties is presented and used to obtain illustrative results. The procedure is based on the measurement of the scattered acoustic field as a function of scattering angle and frequency. Measurements are normalized using analytically determined expressions for emitter and detector beams resulting from a combination of unfocused linear elements arranged in a circular configuration. The spatial effects of finite emitter pulse length and detector gate length are represented by a convolution formula valid for narrow-band transmitted signals and long receiver gates. The normalization includes correction for target absorption as well as measurement of the directly transmitted acoustic power in the free field and yields the average differential scattering cross section per unit volume. Under the Born approximation, this quantity is directly proportional to the spatial-frequency spectrum of the scattering medium inhomogeneities. Measured results are reported for two phantoms consisting of glass microspheres embedded in a weakly absorbing agar background medium. For the phantoms employed, scattering effects, rather than increased absorption, are shown to account for most of the difference in transmission loss between pure agar and agar with glass spheres. The measured differential scattering cross sections are compared with theoretical cross sections for distributions of glass spheres measured experimentally. The measured values show good relative agreement with theory for varying angle, frequency, and phantom properties. The results are interpreted in terms of wave space resolution and the potential for tissue characterization using similar fixed transducer configurations.

ISSN:0001-4966    

DOI:10.1121/1.423033

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

When waves propagate through a medium with smooth velocity perturbations the propagation of wavefronts is determined by the eikonal equation. Here the propagation of wavefronts through a medium with small-scale velocity perturbations is analyzed using the method of strained coordinates. A partial differential equation for the first-order perturbation of wavefronts is derived that includes frequency-dependent wave propagation effects. It is shown that for the special case of the scalar Helmholtz equation with a homogeneous reference medium this leads to the same perturbation of wavefronts as obtained from the Rytov approximation. However, the method presented here can possibly be generalized to more complex wave propagation problems where the Rytov approximation cannot be used, such as the propagation of vector waves.

ISSN:0001-4966    

DOI:10.1121/1.423034

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

Three loss factors are defined for a master harmonic oscillator (HO); the I-loss factor, the U-loss factor, and the effective loss factor. A conductance (β) is conventionally defined as the ratio of the power imparted to a dynamic system by an external drive to the stored energy that this input power generates. The conductance (β) is related to the loss factor (η) by the frequency (ω);β=(ωη).In light of this definition, it is shown that all three loss factors are identical for an isolated master HO at resonance. Differences arise among these loss factors when the master HO is coupled to satellite harmonic oscillators (HO’s). The first two loss factors retain their definitive format in the sense that the stored energy is reckoned only in the master HO; the energy stored in the coupled satellite HO’s and in the couplings is discounted. The effective loss factor, on the other hand, is defined by accounting for the total stored energy that the external drive applied to the master HO generates in the complex. The complex here is composed of the master HO, the satellite HO’s, and thein situcouplings. In those situations in which the portion of the total energy stored in the satellite HO’s and in the couplings substantially exceeds the stored energy in the master HO, the I-loss factor and the U-loss factor may substantially exaggerate the true loss factor of the coupled master HO. Situations of this type are illustrated by data obtained in computational experiments, and it is argued that the true loss factor of the master HO in the complex as a whole is the effective loss factor.

ISSN:0001-4966    

DOI:10.1121/1.423035

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP