摘要:

Over the last several years we have been involved in training high school teachers to use a variety of physics lecture demonstrations. A selection of those dealing with acoustics will be presented. Although intended primarily for high school and college teachers of physics, they should be of general interest to acousticians. [Work supported in part by NSF.]

ISSN:0001-4966    

DOI:10.1121/1.2021582

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

The incremental energy loss ΔE/Eper unit path length for a boundary mode traveling along a rough surface may be calculated from elementary low‐frequency scattering approximations, using previously published results [I. Tolstoy, J. Acoust. Soc. Am.74, 1068–1070 (1983) and72, 960–972 (1982)]. This allows one to calculate explicitly the attenuation factor exp( − δr), whereris the range, withδ = 12ΔE/Efor rough two‐fluid interfaces with arbitrary impedances, constraints, and roughness shapes. It is shown that δ =Af6, wherefis the frequency andAa parameter which depends upon the size, spacing, and form of the roughness (for close‐packed roughness elementsAis proportional to the fifth power of the mean roughness height). Given a point source of sound and a receiver on the rough interface the boundary wave amplitudepB∝r−1/2f3/2exp( − δr) and exhibits, for fixedr, a well‐defined maximum in the frequency domain atfM= (4Ar)−1/6and falls off rapidly for higher frequencies, i.e., it displays a bandpass behavior with slow roll‐off at low frequencies. The predictions of this theory agree with recently reported model work [G.L.D'Spainet al., J. Acoust. Soc. Am., in press]. [Work supported by ONR.]

ISSN:0001-4966    

DOI:10.1121/1.2021583

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

In this paper, we use the extinction theorem to compute aTmatrix which characterizes a given rough interface between two media. In particular, we concentrate on multiple‐layered geometries. Thus we consider an elastic rough infinite slab interfaced with different fluids on either side. This case serves as a model for studying water/ice plate/air systems. Numerical results illustrating the cases of longitudinal or shear wave incidence, as applicable, shall be presented.

ISSN:0001-4966    

DOI:10.1121/1.2021588

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

Pattern recognition application to underwater acoustics is a relatively less explored area, even though much study has been made of sonar signal detection. Recently, significant effort has been made of submarine transient signal analysis and classification. Various spectral and time domain features are considered for detection and event classification. Effective recognition requires signal segmentation. The use of entropy distance measure for waveform segmentation is then examined. The next pattern recognition application is the target motion analysis by using pattern matching idea in the estimation of target range, velocity, and bearing. Another application is in multipath ranging. An image processing technique is used to extract the significant tracks from the correlograms to provide a continuous estimate of time delay or range under a multipath environment. Major computer results reported earlier [C. H. Chen, Pattern Recog. J.16(6) (1983)] along with further results on transient signal analysis are presented. Other applications such as sonar recognition in fisheries are also examined. While the trend continues to be digital processing and system integration, the basic recognition issue remains to be the extraction of effective features from the preprocessed underwater acoustical data. [Work partially supported by NUSC at Newport, RI.]

ISSN:0001-4966    

DOI:10.1121/1.2021598

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

The determination of linguistic structure from surface patterns in text and speech requires the integration of cues from multiple constraint domains including phonetic features, syllable and morpheme structure, syntax, and semantics together with pragmatics. Utilization of these constraints shows that the factors contributing to the integration metric vary along the utterance, and that principled surface variation can be accounted for in terms of these structures, thus reducing the apparent noise. Given the large number of factors that influences the pattern classification decision, it is important to defer commitment to structural hypotheses as long as possible, so that neither “bottom up” nor “top down” search strategies are appropriate models for the recognition of natural language patterns. Instead, observance of cooccurrence relations among the parameters of a model can be exploited in efficient training procedures that extract the maximum amount of information from the experimental corpus. These techniques naturally lead to formulations of constraint domain structures that are mathematically explicit, minimizing the use of heuristics except where dictated by complexity considerations. Experience from contemporary research in speech synthesis and recognition is used to illustrate these principles, characterize current capability, and indicate directions for future research.

ISSN:0001-4966    

DOI:10.1121/1.2021602

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

The low‐frequency form function for plane‐wave scattering by a fluid‐loaded thin spherical shell is characterized by the highQmonopole or “bubble” resonance. As the shell thickness is increased, the monopole resonance is observed to shift to higher frequency and broaden (i.e., theQof the resonance decreases). With a further increase in thickness, highQresonances appear on top of the spectrum of the monopole resonance. These low‐frequency, highQresonances, first reported by Diercks and Hickling [J. Acoust. Soc. Am.41, 380–393 (1967)] have never been satisfactorily explained. In this paper we present the results of our investigation, based upon the linear theory of elasticity, of these highQresonances. The dependence of the resonances on frequency, and shell and fluid parameters are presented along with the elastic stresses and displacements in the shell. Dispersion curves are generated from numerical solutions and a physical explanation for the strong coupling to the fluid medium is obtained.

ISSN:0001-4966    

DOI:10.1121/1.2021607

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

The propagation of acoustic waves on the cylindrical boundary between the core and cladding materials of a clad rod waveguide is described. Typically, axisymmetric torsional, axisymmetric radial‐longitudinal, and core‐guided shear modes may propagate within a rod of cylindrical cross section if the velocity of plane shear waves in the cladding material exceeds the velocity in the material of the core [R. N. Thurston, J. Acoust. Soc. Am.64, 1 (1978)]. If instead the elastic constants of the core and cladding materials of the rod are reversed so the material with the slower shear wave speed is on the outside, no modes are supported within the core but an interface wave can exist on the core‐cladding boundary. In this paper the transmission properties of an all glass clad rod with a suitable core‐cladding elastic constant relationship to support non‐attenuating interface waves are discussed. The resulting improved freedom from spurious responses allowed by this single mode operation is discussed. [Work supported by NASA.]

ISSN:0001-4966    

DOI:10.1121/1.2021611

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

The aerodynamic sound generated by a small scale wing model interacting with a 4‐in. jet has been investigated experimentally in NASA‐AMES anechoic chamber. The investigation consists of two parts. The first part is concentrated on the jet shear layer/wing interaction noise. The second part is the study of noise associated with separated flow. Cross‐correlation techniques are used to discriminate against unwanted noise. The results of experiment 1 show that the sound generated by shear layer/wing interaction is 10 dB higher than the free jet noise. A round guide attached to the jet exit reduced the farfield sound by 8 dB. The rms pressure in the nearfield is found to be inversely proportional to the third power of the distance from generating eddies. The typical Strouhal number of sound generated, based on the shear layer thickness and the mean flow speed, is 0.17. The results of the sound experiment show that on the separation side of the wing the generating eddies are located near the trailing edge, as expected. The noise generating eddies propagate downstream with the convection velocity and are not triggered until they reached the trailing edge. The convection speed is found to be 0.85 times the jet mean flow speed, as judged by signal time delays.

ISSN:0001-4966    

DOI:10.1121/1.2021619

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

Using the recently developed two‐microphone technique of acoustic intensity measurement, radiation efficiencies of a single panel and individual panels of a complete vehicle structure have been made under controlled, laboratory conditions. The data obtained from the single panel were used to develop measurement techniques and study the sound field near the panel. Radiation efficiencies of the vehicle structure were used along with measured vibration response obtained under normal operation conditions to determine the sound power produced by each individual panel. Results describing the technique development and the application to the vehicle structure are presented in this paper.

ISSN:0001-4966    

DOI:10.1121/1.2021631

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

The dominance of one ear over the other in the perception of pitch of dichotic chords has been reported by Efron and Yund [J. Acoust. Soc. Am.59, 889–898 (1976)] and in subsequent studies by that group. The present investigation addressed the existence of correlations between psychophysical and electrophysiological asymmetries. Specifically, the relation between ear dominance measured psychophysically using the Efron paradigm and right‐left asymmetries in middle latency auditory evoked potentials was examined in ten normal‐hearing adult subjects. Absolute and interwave latencies were obtained for middle latency responses to right and left monaural, binaural, and dichotic presentation conditions using tonal stimuli. Rank order correlation coefficients were used to compare right‐left ear and hemifield evoked potential latency differences to measures of ear dominance. Results indicated that latency measures, particularly for components involving wavePbof the middle latency response, correlated with the direction of ear dominance. The characteristics of these correlations will be discussed. [Supported by NINCDS ♯NS 11647, the Louisiana Lions Eye Foundation, and the Eye and Ear Foundation.]

ISSN:0001-4966    

DOI:10.1121/1.2021635

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP