摘要:

In any approach to calculation of the wall pressure spectrum of a TBL based on an inhomogeneous (Lighthill) wave equation, singularities of the spectral density arise along various lines or surfaces in (k,ω) space. These lines of surfaces correspond to the acoustic or structural dispersion relations, and the singularities may be controlled by such mechanisms as surface finiteness, dissipation in the structure or fluid, and surface compliance. This paper will examine the way in which these various mechanisms control the singularities in different regimes of the spatial and dynamical parameters involved, and will give scaling laws for the pressure spectral densities at the critical conditions in (k,ω) space. [Work supported by ONR, Code 425.]

ISSN:0001-4966    

DOI:10.1121/1.2022335

出版商:Acoustical Society of America    

年代:1985

数据来源: AIP

摘要:

The wavenumber‐frequency structural response of a fluid‐loaded, periodic ring‐supported, circular cylindrical shell is modeled. In the model, the ring supports are assumed to interact with the shell only through normal forces. The TBL pressure fluctuation wavenumber‐frequency spectra models of Corcos [J. Fluid Mech.18, 353–378 (1964)] and Chase [J. Sound Vib.70, 29–67 (1980)] are used in this effort. Sums are taken over wavenumbers to obtain predictions of the average shell response to TBL excitation as a function of frequency. Bands of wavenumbers that control the shell response are identified for different frequencies and shell configurations.

ISSN:0001-4966    

DOI:10.1121/1.2022338

出版商:Acoustical Society of America    

年代:1985

数据来源: AIP

摘要:

Since research in this area is relatively recent, an informal discussion period is planned for those interested in exploring and sharing experiences in the progress, problems, and potentials of modal and finite‐element analysis applied to musical instruments.

ISSN:0001-4966    

DOI:10.1121/1.2022346

出版商:Acoustical Society of America    

年代:1985

数据来源: AIP

摘要:

The diffraction of a Gaussian ultrasonic beam in absorbing fluids has been shown to produce a Gaussian field distribution in the fundamental component [J. Acoust. Soc. Am. Suppl. 176, S23 (1984)]. Now we have derived an analytical expression for the second harmonic and find that it also is a Gaussian function in the quasilinear approximation. Our expressions for the second harmonic also are free of the nearfield oscillations characteristic of the radiation from a piston transducer [cf. S. I. Aanonsen, T. Barkve, J. N. Tjøtta, and S. Tjøtta, J. Acoust. Soc. Am.75, 749 (1984)]. Calculated results are compared with measurements taken with the Gaussian transducer described previously. Reasonable agreement between theory and experiment are found for both the fundamental and the second harmonic of an initially sinusoidal Gaussian ultrasonic beam in water at 2 MHz. [Research supported in part by the Office of Naval Research.]

ISSN:0001-4966    

DOI:10.1121/1.2022349

出版商:Acoustical Society of America    

年代:1985

数据来源: AIP

摘要:

The Boltzmann‐Ehrenfest adiabatic invariance formalism used to derive the acoustic radiation stress equation for solids [J. H. Cantrell, Jr., Phys. Rev. B30, 3214 (1984)] is combined with recent developments in stochastic classical dynamics to obtain the internal and Helmholtz free energies in terms of random zero‐point nonlinear acoustic modes. The results lead to an expression of the thermal expansion coefficients of crystalline solids in terms of nonlinearity parameters related directly to the acoustic radiation‐induced static strains. When the model acoustic non‐linearity parameters are set to zero, the internal energy expresionreducesto the Planck radiation law obtained from quantum mechanics. If, in addition, the quasiharmonic assumption is invoked for the model frequencies, the thermal expansion equationreducesto that obtained from Debye‐Grüneisen‐Einstein statistical model of a system of quantum oscillators.

ISSN:0001-4966    

DOI:10.1121/1.2022354

出版商:Acoustical Society of America    

年代:1985

数据来源: AIP

摘要:

Four human observers were run in a two‐alternative, forced choice procedure to measure the detectability of a 500‐Hz tone in the presence of each of 25 digitally generated, 100–3000 Hz maskers. The masker was randomly selected on each trial within blocks of 80 trials. The average percentage of correct responses across all maskers was within the range usually reported. The percentages for the individual maskers varied from chance to near perfect, however. The three maskers which led to the best detection and the three which led to the worst detection were used in the second portion of the study to stimulate low‐frequency, auditory‐nerve fibers of the chinchilla. Fifty presentations of each signal and masker combination were used to obtain spike rates and phase‐locking measures. These results are compared with those obtained from the first portion of the study and with measures of the physical characteristics of the stimuli. [Supported by NIH Grant Nos. NS1928 and NS16396.]

ISSN:0001-4966    

DOI:10.1121/1.2022362

出版商:Acoustical Society of America    

年代:1985

数据来源: AIP

摘要:

A simple extension of the Webster‐Jeffress model of the BMLD is presented with its predictions for (1) the effects of various stimulus parameters on the size of the BMLD, (2) the relative size of the BMLD in simultaneous and post‐masking, and (3) the dependence of the BMLD on differences in frequency between the signal and masker. Data illustrate the high correlation between observers' sensitivity to level differences and their sensitivity to interaural delay. The attentuation characteristic of the interaural‐delay‐tuned mechanisms responsible for the BMLD is also illustrated.

ISSN:0001-4966    

DOI:10.1121/1.2022365

出版商:Acoustical Society of America    

年代:1985

数据来源: AIP

摘要:

The logarithmic spiral (base 2) offers a simple passive means of detecting the regularity observed in the streams of nerve pulses produced when phase locked fibers respond to periodic sounds. That is, if time is wrapped into a spiral with time zero at the spiral's origin, then when nerve pulses‐flow outwards along the path of the spiral, the pulses of a regular stream will coalesce onto spokes emanating from the center of the spiral once per cycle. The spoke pattern has a fixed shape and it rotates around the spiral as the periodicity of the pulse stream varies. Secondary units can be used to detect coalescence on spoke patterns with specific orientations and so convert the temporal pitch information into spatial pitch information. The spoke pattern completes one revolution as the pulse rate rises or falls an octave, and the primary intervals of the Just diatonic scale produce the simplest combined spoke patterns. Thus, the logarithmic spiral provides a basis for a temporal model of pitch perception which can also predict musical harmony.

ISSN:0001-4966    

DOI:10.1121/1.2022379

出版商:Acoustical Society of America    

年代:1985

数据来源: AIP

摘要:

The use of microelectrode mapping methods, in conjunction with studies of cortical architecture, patterns of connections, and the response properties of single neurons, has led to a greatly increased understanding of the functional organization of somatosensory cortex in mammals. All mammals appear to have the traditionally defined first and second somatosensory representations, SI and SII, but at least some mammals have additional body representations as well. Furthermore, the area traditionally regarded as “SI” in monkeys actually includes four functionally distinct representations. Within “SI,” four striplike architectonic fields, areas 3a, 3b, 1, and 2 have long been recognized. It is now clear that areas 3b and 1 form separate parallel and largely mirror‐image representations of the body surface, each with major inputs from a single representation of the body surface in the ventroposterior nucleus (VP) of the thalamus. VP appears to relay information from both slowly and rapidly adapting peripheral neurons to area 3b, while information from rapidly adapting neurons is relayed to area 1. Neurons with properties that could reflect Pacinian receptor influences are found in area 1, but not area 3b. The anatomical pathways mediating Pacinian‐like responses are unknown. Area 3a contains a representation of largely deep receptors, probably muscle spindle afferents, relayed from part of the thalamus dorsal to VP. Area 2 forms a representation of both deep and cutaneous body receptors. The somatosensory cortex receives input from other regions as well, including the anterior pulvinar and ventroposterior inferior nucleus of the thalamus. Other portions of the somatosensory cortex are less well understood.

ISSN:0001-4966    

DOI:10.1121/1.2022383

出版商:Acoustical Society of America    

年代:1985

数据来源: AIP

摘要:

Intracellular recording followed by tracing with intracellular dye has revealed that afferent saccular axons of the bullfrog (Rana catesbeiana) are acutely responsive to substrate‐borne vibrations, with linear gain up to 3000 spike/s (neural response) per cm/s2(seismic amplitude). Eighth‐nerve (presumedly saccular) axons from the white‐lipped frog (Leptodactylus albilabris) show even greater seismic sensitivity, with linear gain up to 20 000 spikes/s per cm/s2(up to 70 spike/s per Angstrom of vibrational displacement). In both species, the sensitivity frequency range matches well the principal spectra (approximately 10–300 Hz) of slow seismic waves (Rayleigh and Love waves) in moist soil. In synchrony with its airborne call (a 40‐ms chirp), the male white‐lipped frog often produces a seismic thump—with strong Rayleigh‐wave and Love‐wave components (peak accelerations ∼2 cm/s2at a distance of 1 m from the frog) in the moist soil from which it calls. The thump waveforms match those produced by impulselike impacts on the soil surface, with spectra matching the frog's seismic sensitivity. Even in the absence of chirps, thumps provide male‐male interaction responses in male white‐lipped frogs. [Work supported by NSF (ERL) and NIH (PMN).]

ISSN:0001-4966    

DOI:10.1121/1.2022385

出版商:Acoustical Society of America    

年代:1985

数据来源: AIP