摘要:

The relationship between the density of hair cells (cells/mm) and measured distance along the guinea pig organ of Corti was determined using light microscopy and the surface specimen technique. It was demonstrated that the density of inner hair cells (IHC; mean 92.0±2.4) and 1st row of outer hair cells (OHC1; mean 118.7±2.3) did not show significant variation along the organ of Corti except within 0.5–1.0 mm of the apex and base where there was considerable variation between animals in the density of cells. There was a close relationship between the accumulated number of either IHC or OHC1and distance from the base along the organ of Corti. Distances estimated by hair cell counts were similar to those determined by direct measurement. It is concluded that hair cell counts can be used to reliably estimate distances along the organ of Corti where accurate direct measurement is not possible, such as in scanning electron microscopy.

ISSN:0001-4966    

DOI:10.1121/1.391136

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

Spontaneous oto‐acoustic emissions (OAEs) were measured prior to, during, and following administration of aspirin. The dose schedule was three 325‐mg tablets every 6 h for a total of 16 doses (3.75 days). In every subject studied, all spontaneous OAEs gradually diminished and then disappeared during the drug regimen. Emissions that were initially small disappeared within 14–20 h of beginning the drug regimen (3–4 doses), while initially large emissions took 40–70 h (7–12 doses) to disappear completely. In contrast, the initial size of an emission appeared unrelated to the time required for it to recover to full strength once drug administration ceased. The recovery process was highly idiosyncratic, with the emissions of some subjects returning to full strength within 24 h, while for other subjects, full recovery required several days. In two subjects having multiple emissions in the same ear, the relative sizes of the different emissions often changed greatly during the disappearance and recovery phases. When small frequency shifts appeared for these subjects, they appeared—and were in the same direction—for each of the multiple emissions. In a related experiment, the spontaneous emission was unchanged in one subject who took a drug that inhibits the intracellular entry of calcium ions (verapamil).

ISSN:0001-4966    

DOI:10.1121/1.391585

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

Evoked potentials to a dichotic stimulus composed of either (1) two binaurally presented tone pips or (2) one tone pip and an electrical pulse to the auditory nerve are recorded from the primary auditory cortex of barbiturate anesthetized cats. The composite stimulus is delivered as a time delayed pair where the interstimulus interval (25 ms) is within the relative refractory period of the evoked potential to either stimulus alone. The amplitude of the cortical potential to the trailing stimulus is compared with its single stimulus amplitude as the frequency of the trailing tone pip is changed from 250 Hz through 40 kHz. There is an optimal frequency range over which the trailing stimulus is suppressed and this range appears directly related to the current of a preceding electrical pulse. The frequency of maximum suppression shifts according to the position of the electrode in the nerve. In some experiments secondary maxima develop, suggesting stimulus current spread from fibers of one cochlear turn into fibers from another turn.

ISSN:0001-4966    

DOI:10.1121/1.391586

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

The influence of varied linear array configurations on passive ranging is determined when imperfect measurements of the time delays between the sub‐arrays are available. The exact bias and farfield bias and variance relations on the source range estimates are derived as a function on unequal sub‐array separation. The results are contrasted with those found in the literature on equally separated sub‐arrays to highlight the sensitivity and resulting degradation in performance. It is found, for instance, that the range bias more than doubles when the internal sub‐array is moved from the midpoint to the quarter‐point from either end sub‐arrays and more than quadruples when it is moved from the quarter‐point to the one‐eighth‐point. Since the range variance is related to the true range and to the incurred bias, it degrades much more rapidly. The commonality between array ranging and multipath ranging is also developed for various channels of interests. The optimal placement for the receiving sensor in multipath channels is derived. Though it turns out that the same relations apply to both ranging problems, the existence of a multipath channel will support a longer ranging capability with the baseline now effectively determined by such large parameters as water depth, receiver, and source depths. Such results enable the merger of multisensor data according to their individual merits and the provision for a credence estimate of the source range choice.

ISSN:0001-4966    

DOI:10.1121/1.391587

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

A readily steerable, ambiguity‐free beam is formed in real time from a receive aperture containing a sparsely populated array of transducer elements with selected spacings. The system approach utilizes multiple phase‐matched local oscillators in the process of producing at an IF a full set of synthetic spatial frequencies which are similar to the actual spatial frequencies associated with all conventional apertures. A summation of these synthetic spatial frequencies produces the scannable beam with at least as much resolution and freedom from interference as that obtainable from the same size aperture fully filled with closely spaced elements. Beam formation is accomplished either within the system by using a beam forming network or externally by applying the synthesized spatial frequencies to a fully filled transmit array of elements (an autonomous retrodirective system). Experimental measurements at a rf demonstrate that the principles are valid. Superdirectivity, circular arrays (for cylindrical coverage), self‐steering arrays, real‐time holography, passive distance measurement, and frequency/phase modulation recovery from incident carriers are possible extensions of the system approach.

ISSN:0001-4966    

DOI:10.1121/1.391588

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

The generation and some relevant properties of a class of periodic pseudorandom sequences called the maximum‐length sequence is described briefly. A simple and practical method is proposed to resolve a technical difficulty in using these sequences with FFT processing. The potential advantage of using a maximum‐length sequence as a test signal for architectural acoustic measurements is discussed and illustrated by an example.

ISSN:0001-4966    

DOI:10.1121/1.391153

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

The one‐dimensional model of the concentric‐tube resonator [J. W. Sullivan and M. J. Crocker, J. Acoust Soc. Am.64, 207–215 (1978)] assumes that (1) the impedance of the perforation is constant along the length of the flow tube and (2) spatial variations of acoustic pressure in the transverse direction of either tube or cavity are small. Some recent measurements on long resonators have indicated that when mean flow is present, net flow in the cavity, although small relative to that in the tube, affects the impedance in a bidirectional manner resulting in violation of assumption 1. Experiments using microphone probes have demonstrated the validity of assumption 2 provided the tube is perforated axisymmetrically and uniformly. When this is not the case, a circumferential cross mode can be induced which invalidates the one‐dimensional model.

ISSN:0001-4966    

DOI:10.1121/1.391589

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

Three hearing protection devices [Siebe Norton Com‐fit earplug, Flents Silenta model 080 earmuff, and E‐A‐R■foam earplug] were compared for their effectiveness in preventing both daily temporary threshold shifts (TTS) and threshold variability between sequential annual audiograms for workers in an industrial environment with a TWA of 107 dB. Com‐fit wearers showed significant TTS at 500–4000 Hz from the beginning to the end of the workday. Silenta wearers displayed significant TTS at 500 Hz and nonsignificant improvement at 6000 Hz. E‐A‐R wearers showed significant TTS at 1000–2000 Hz and nonsignificant improvement at 3000–6000 Hz. Statistical analysis indicated that the protection provided by the E‐A‐R plug was significantly better than that of the Com‐fit plug at 500–4000 Hz, and significantly better than the protection of the Silenta muff at 500, 3000, and 4000 Hz. Employees’ last four annual audiograms prior to the start of the TTS study were evaluated to compare the wearer groups’ mean values of the %BWs statistic (sequential percent better or worse). Previous research indicates that the %BWs statistic for a properly protected population with past audiometric test experience will be less than 30%. The E‐A‐R group showed an acceptable %BWs value (26%), but the Silenta wearers (45%) and Com‐fit wearers (53%) showed excess threshold variability in threshold measurements from year to year.

ISSN:0001-4966    

DOI:10.1121/1.391590

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

An ultrasonic spectroscopy technique for the simultaneous, wideband measurement of attenuation and dispersion in solids is described. The technique is based on Fourier analysis of digitized ultrasonic waveforms. Results are compared with discrete frequency measurements of these properties with good agreement observed.

ISSN:0001-4966    

DOI:10.1121/1.391591

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

A train of 1‐MHz pulses can generate maxima of cavitation activity [V. Ciaravino, H. G. Flynn, and M. W. Miller, Ultrasound Med. Biol.7, 159–166 (1981)] at pulse lengths of 6 and 60 ms and at pressure amplitudes,PA, between 5.4 and 9.4 bars (or intensities between 10 and 30 W/cm2). Generation of maxima atPAbetween these limits on pressure amplitude implies that the increase in cavitation activity originates from gas nuclei with radii lying in a critical size range centered at about 0.08 μm. The mechanism proposed for this phenomenon suggests that nuclei in this critical range are unstabilized nuclei generated in one pulse and surviving to the next with an appreciable fraction of the survivors lying in the critical range. Transient cavities that grow from such small nuclei are shown to behave as isolated mechanical systems that on reaching maximum size collapse as imploding spheres. The maximum pressures reached in such imploding cavities would then approximate those calculated for the spherical collapse of cavities. The occurrence of the observed maxima is ascribed to the spherical collapse of transient cavities.

ISSN:0001-4966    

DOI:10.1121/1.391592

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP