摘要:

A modified technique is presented for determining the physical properties of individual microparticles such as biological cells. Two submerged confocally positioned transducers (one transmitter/receiver and one receiver) generate 30‐MHz center frequency tone bursts which scatter off of single particles convected by a coaxial jet flow. The scattered pressure is measured at 90° and 180°, analog envelope detected, digitized, and stored in computer memory. By employing a long wavelength acoustic scattering theory first developed by Raleigh, it is possible to calculate the particle density and compressibility givena prioriknowledge of both the particle volume and the physical properties of the host liquid. This apparatus, which is still in the developmental stage, is simpler and more versatile than an earlier, three‐transducer system developed by Mark Roos [Doctoral dissertation, Yale University (1983)]. The system performance and theoretical scattering model are evaluated using calibration particles (e.g., polystyrene spheres, liquid drops) and biological cells. [Work supported by NIH through grant number R01‐GM30419 and by ONR.]

ISSN:0001-4966    

DOI:10.1121/1.2022228

出版商:Acoustical Society of America    

年代:1985

数据来源: AIP

摘要:

Experimental results are presented for the scattering of an ultrasonic pulsed beam (f= 1.90 MHz, τ = 200 μs) interacting in the presence of a submerged water jet (diam = 4.8 cm, Re≃5×105). The transmitting 2.54‐cm‐diam PZT transducer unit is located 20 nozzle diameters down‐stream from the jet orifice and is positioned 1 m from the symmetry axis of the jet. The unit is supported by a radius arm so that the incident beam is free to rotate 360° about the symmetry axis of the jet. A 2.54‐cm‐diam stationary receiving unit located 2 m from the jet axis detects the scattered energy pulses. Experimental results are reported for both the scattered energy and the spectral broadening of the incident pulse versus scattering angle. Due to the very short wavelength of sound and relatively large interaction volume of the turbulence the classical scattering theories of Lighthill, Kraichnan, Batchelor, and others, which are valid in the Born approximation, cannot be applied here. Theoretical scattering models including the effects of multiple scattering are discussed using some of the recent theoretical results of R. L. Fante [Radio Sci.17(3), 1521–1530 (1982)]. [Work supported by NRL (Physical Acoustics Branch) and USNA.]

ISSN:0001-4966    

DOI:10.1121/1.2022230

出版商:Acoustical Society of America    

年代:1985

数据来源: AIP

摘要:

We demonstrate a measurement technique to determine the structure‐borne intensity (power flow) in a point‐driven, fluid‐loaded, homogeneous thin plate. This intensity is uniquely determined from a knowledge of the normal velocity of the surface of a sinusoidally driven plate. A noncontact method is presented which uses a scanning hydrophone to measure the pressure in a plane very close to the source. It is shown how this pressure measurement is sufficient to compute the two‐dimensional structural intensity vector inside the plate. Furthermore, these vectors are used to compute the power injected into the plate from a point driver. Independent measurement of injected mechanical power is shown to be in close agreement. A comparison of the structure‐borne intensity with the acoustic intensity radiated into the medium indicates that structual intensity is much more accurate in locating the real source than the acoustic intensity, the latter often failing completely. The examples given in this paper are for a source underwater, but the technique applies without modification to plate sources in air.

ISSN:0001-4966    

DOI:10.1121/1.2022237

出版商:Acoustical Society of America    

年代:1985

数据来源: AIP

摘要:

The importance of the spatial extent of applied forces in the radiation of sound from structures was studied through formulation of the sound power radiated by a line force acting on a infinite elastic beam. The expression for sound power was integrated numerically and the results examined as a function ofkL, the acoustic length of the force, and the wavenumber ratio. Below coincidence the power was found to be generally proportional to (kL)−2. Near and at coincidence, sufficiently large force scales produced a significant effect on the power. In particular, when the length of the force corresponded to an integral multiple of the critical wavelength, the coincidence peak was completely suppressed. Above coincidence, minima in the sound power occurred when the force length was a multiple of the wavelength of the free bending wave. These minimal values of power were shown to be nearly equal to the power radiated far below coincidence. These results are discussed in terms of the coupled structural‐acoustic wavenumber response function and the wavenumber spectrum of the applied force. [Work supported by NSF.]

ISSN:0001-4966    

DOI:10.1121/1.2022241

出版商:Acoustical Society of America    

年代:1985

数据来源: AIP

摘要:

In the past, most studies of the effects of fluid loading on the response of time harmonic line forced plates have involved either “ad hoc” simplifications whose adoption was justified on physical grounds alone or numerical techniques and restricted frequency ranges below the “coincidence” frequency. We use the method of Matched Asymptotic Expansions (MAE) to obtain a series ofsimpleanalytic expressions which cover overlapping regions of the whole frequency range. A composite expression is easily formed for the radiated power. This gives a simple single expression,uniformly validfor all frequency ranges, and yields predictions for the radiated power in good agreement with the corrected curves of Nayak [J. Acoust. Soc. Am.49, (1979)]. [Work supported by ONR Code 425.]

ISSN:0001-4966    

DOI:10.1121/1.2022245

出版商:Acoustical Society of America    

年代:1985

数据来源: AIP

摘要:

Listeners were presented a randomized list of /bVs/, /dVs/, and /gVs/ syllables produced by two male talkers and were instructed to press a response key immediately upon recognizing a particular initial stop consonant. Three groups of 12 subjects were monitored for /b/, /d/, and /g/, respectively. The test syllables contained 10 English monophthongs varying substantially in intrinsic duration. Reaction times to the initial consonants correlated positively with the duration of the following vowels. For both talkers' syllables, this correlation was higher for initial /d/ and /g/ (withrvalues ranging from 0.41–0.67) than for initial /b/ (withrvalues ranging from 0.28–0.39). These results support the view that consonant recognition is vowel dependent and, specifically, that a certain proportion of the vowel formant trajectory must be processed before consonants can be reliably decoded. [Work supported by NICHHD.]

ISSN:0001-4966    

DOI:10.1121/1.2022252

出版商:Acoustical Society of America    

年代:1985

数据来源: AIP

摘要:

Vowels are longer before voiced consonants than before voiceless consonants, and a number of studies have demonstrated that perception of voicing, in syllable‐final and intervocalic positions, is in accordance with this production regularity. We present a study, using nonspeech stimuli, that suggests that this agreement between production and perception for segmental duration is grounded in auditory processing of complex stimuli in general. Two types of square‐wave analogs, modeled after a speech series ranging from “aba” to “apa” were constructed. The two nonspeech stimulus series varied in duration of a silent interval from 20–110 ms bounded by frequency transitions out of and into steady‐state segments. One series had an initial segment duration of 155 ms, whereas, the initial segment duration of the other series was 245 ms. Duration of the final segment was 188 ms for both series. Listeners judged significantly more of these nonspeech stimuli to be similar to the short silent interval endpoint when the initial segment was long than when the initial segment was short. This result parallels the finding for speech that listeners perceived more voiced /b/ than voiceless /p/ consonants following longer vowels. These results call into question explanations of this production/perception concordance that suggest either mediation of perception by knowledge of production regularities, or direct perception or articulation. [Work supported by NICHHD.]

ISSN:0001-4966    

DOI:10.1121/1.2022257

出版商:Acoustical Society of America    

年代:1985

数据来源: AIP

摘要:

The goal of this experiment was to compare the representation of speech sounds obtained using psychoacoustical measurements with those furnished by the model of the peripheral auditory system developed by Delgutte [inRepresentation of Speech in the Peripheral Auditory System, edited by R. Carlson and B. Granström (Elsevier, New York, 1982), pp. 131–149]. We studied the perceptual representation of the initial 16 ms of the burst of the consonant /k/, in three vocalic contexts /a/,/i/, and /u/, using ipsilateral simultaneous masking. The masker was one of the three VCV sequences /aka/, /iki/, and /uku/, extracted from natural speech. The test sound was a tone burst with a duration of 16 ms and with a fixed frequency ranging from 0.840–3.400 kHz, by critical‐band steps. The test tone was located just at the beginning of the burst. The registered level of the just‐audible test tone allows one to obtain the “psychoacoustical” spectra of the beginning of the consonant burst for the three vocalic contexts. These spectra will be compared with the LPC spectra of the same portion of the signal and with “model rate profiles” (i.e., simulated average discharge rate as a function of the characteristic frequency) obtained at the output of Delgutte's model. This comparison allows for a first pyschoacoustical calibration of the model adapted to the study of speech sounds.

ISSN:0001-4966    

DOI:10.1121/1.2022261

出版商:Acoustical Society of America    

年代:1985

数据来源: AIP

摘要:

Interpretation of attenuation measurements in the Baltic Sea [H. G. Schneider, R. Thiele, and P. C. Wille, J. Acoust. Soc. Am. (to be published, 1985)] indicates a need for estimating sound absorption in low salinity waters. While the magnesium sulfate component depends simply on the first power of salinity, the low‐frequency boric acid relaxation is more complex. The mechanism involves exchange with carbonate in which the ion‐pair calcium carbonate affects only the absorption magnitude αmax. Absorption measurements by the resonator method (at elevated boric acid concentrations) show roughly 0.5 power dependence on calcium concentration in the range of interest. The Baltic salinity is roughly14normal while the carbonate and acidity (pH≃8.0) are both normal. Since αmaxdepends on the concentration product,S1.5dependence gives a reduction by the factor 8 which makes it negligible. The relaxation frequencyfrdepends on a sum of concentrations and is estimated to be reduced by the factor 1.6. Laboratory measurements offrin Baltic water samples by the temperature‐jump method show reasonable agreement. We conclude that the boric acid relaxation probably plays no role in Baltic Sea attenuation.

ISSN:0001-4966    

DOI:10.1121/1.2022269

出版商:Acoustical Society of America    

年代:1985

数据来源: AIP

摘要:

The distribution of travel time for pulses propagating through a random ocean is obtained. The difference between distributions obtained by weighting each pulse with its intensity, or plotting a histogram of the number of pulses regardless of intensity, is discussed. The difference between distributions obtained for discrete scattering media such as particulates, and continuous media such as an internal‐wave field, is discussed. These results have relevance to the use of travel‐time observations to determine the statistical characteristics of random media, such as in internal‐wave acoustic tomography. They also relate to mesoscale tomography, in that internal waves introduce a bias of order 10 ms for 1000‐km rays in the ocean. [Supported by DARPA and ONR.]

ISSN:0001-4966    

DOI:10.1121/1.2022275

出版商:Acoustical Society of America    

年代:1985

数据来源: AIP