bluuebunny/crossref_metadata_2025 huggingface dataset:
Interpretation of Propagation Measurements at a Variety of Shallow Water Sites
Authors: Daintith M. J. , Dunn D. J. , Roebuck I.
Published: October 2005

The paper describes shallow water measurements of propagation loss using explosives as sources, and omnidirectional hydrophones as receivers. Several sets of measurements in isothermal water in the North Sea, with bottom types varying through mud, sand, and gravel to rock outcrops, appear to give very similar absolute levels of loss (as measured from the pressure peak level received). A different series of measurements in the Mediterranean, where three runs were made at the same place in differing bathythermal conditions, showed considerably varying levels, and also significant dependence of received levels on the depth of the receiving hydrophone and the source charge as distinct from the North Sea sites, where in isothermal conditions the field appeared to be uniform throughout the water depth. The chief effect of the composition and roughness of the seabed appears to be in determining the elongation and distortion of the signals. In one area, returns of over I sec in duration have been received. The paper also includes a Short review of the philosophy behind the use of explosives for shallow water research and an outline of theoretical work using the “impulse response” approach.
Calculation of Natural Frequencies of Composite Shells
Authors: Rand R. A. , Shen C. N.
Published: October 2005

A new technique for calculating the natural frequencies of composite shells was developed. The technique is based upon the finite element method of structural analysis and Rayleigh's principle, which is applied directly to shell structures for the first time. Because the element developed is applicable to anisotropic shells of arbitrary shape, the technique is very general. By using Rayleigh's principle the necessity of assembling over all mass and stiffness matrices for the structure and solving the resulting characteristic equation is eliminated; frequencies are calculated using elemental mass and stiffness matrices directly. Thus the technique is very efficient from a computational standpoint. It is made even more efficient by using a special mass matrix which is a hybrid between a lumped and a distributed mass matrix. Another unique feature is that prior information regarding the modal vectors can be used directly to decrease the computational time.
Vibration Analysis of Thick-Walled Spheres and Cylinders
Authors: Rose J. L. , Chou S. C. , Chou P. C.
Published: October 2005

A wave propagation approach is employed to determine the fundamental frequency of hollow spheres and long hollow cylinders. The study was initiated in order to study the periodic response of such specimens as a function of the number of wave reflections off the inner and outer surfaces as well as the thickness-to-inside radius ratios (h/Ri). It was hoped to achieve a relationship similar to that obtained in the classical longitudinal step loading bar problem. In the bar case, the material response is periodic for either two or four complete reflections, depending on whether the bar has a free or a fixed end. In the hollow sphere and cylinder problem, however, the analysis is not as simple. The motion is approximately periodic. It was found that the number of wave reflections for one cycle was some irrational number, the number being a function of (h/Ri). This unusual observation led to the development of useful design curves and equations determining the fundamental frequencies of thick-walled spheres and cylinders. Comparisons of results from the vibration and wave propagation approaches are used to establish regions of validity of the approaches as a function of (h/Ri).
Vibration of Beams and Plates with Boundary Stiffness and Damping
Authors: Faulkner L. L.
Published: October 2005

An analytical method of predicting the mode shapes and natural frequencies of vibration for continuous structures with elastic edge constraints is presented. The method consists of formulating dynamic edge receptances for the structure using classical solution techniques and matching the receptance of the structure with the receptance of the constraining boundary. The technique is illustrated by the solution of a beam and a circular plate with elastic boundaries and with boundary damping. A discussion is presented giving the influence of the boundary conditions on the vibration of the structure. These examples show numerically the effect of elasticity of the support on the resonant frequencies and mode shapes of the structure. Parameters are obtained which indicate when one may assume simply supported or clamped boundaries for the actual case of elastic boundaries without introducing large errors in the natural frequency or mode shape.
Simple Thickness Modes for Laminated Composite Materials
Authors: Thomas C. R.
Published: October 2005

The simple thickness modes for laminated media with layering both parallel and perpendicular to the plate-free surfaces are studied according to the “effective stiffness” theory and the results obtained are compared with results found from the effective modulus” theory. The importance and effects of the number of layer pairs for layering parallel to free surfaces and of the ratio of plate thickness to the thickness of a layer pair for layering perpendicular to free surfaces on dimensionless “effective stiffness” frequencies are considered. The various “effective stiffness” and “effective modulus” frequency equations have been solved for a stiff-matrix-stiff-reinforcing layer material and for a soft-matrix-stiff-reinforcing layer material, the results are presented in graphs depicting the variation of dimensionless frequency with changes in dimensionless thickness ratio.
Power Flow between Two Coupled Beams—Impulse Response Function Method
Authors: Tucker A. J. , Maidanik G.
Published: October 2005

Crandall and Lotz [J. Acoust. Soc. Amer. 49, 352–356 (1971)] and more recently Davies [81st Meeting of Acoustical Society of American, Washington, D. C., 20–23 April 1971, J. Acoust. Soc. Amer. 50, 96(A) (1971)] evaluated the power flow between two coupled simply supported beams. The coupling is achieved by a rotational spring; this type of coupling renders the coupling terms in the equation of motion simple. The works referred to employed the differential operator method of evaluating the power flow between the two beams. In this paper the evaluation of the power flow employs the impulse response functions of the beams. Although the results are, by and large, similar to those obtained by the referenced authors, the impulse-response function method possesses some distinct advantages. One of these advantages is that the impulse-response function need not be expressed in terms of modes; it may be stated by an expression consisting merely of four terms.
Experimental Investigation of the Vibrational Characteristics of Truck Tires
Authors: Reiter William F. , Hart F. D.
Published: October 2005

At speeds in excess of 40 miles/h, tire noise usually predominates the over-all noise produced by truck traffic. One of the sound-producing mechanisms of the tire is the vibration of the tread and tire casing. In order to relate the external parameters of tire load, pressure, speed, tread types, etc., with the noise produced through tire vibration it is essential to define the tire vibrational characteristics. The object of this experiment was to obtain the data necessary to describe the vibrational behavior of a truck tire. Data are presented showing the effects of pressure, tread, and load on frequency and mode shapes, in addition to the relationship between sidewall and tread vibrations for a typical truck tire. [NASA and NSF are acknowledged for partial sponsorship of this work.]
Impulse-Response Function of Periodically Supported Systems
Authors: Maidanik G. , Tucker A. J.
Published: October 2005

A number of works have recently appeared dealing with the response of homogeneous structural systems to which are attached line or point impedances at periodic intervals. In most of these works the analyses were performed in a form that mixes the spatial-vector and wave-vector domains. (The domains are related by a Fourier transformation.) Indeed, as a result of the mixture, it becomes necessary either to rely on heuristic arguments concerning the response or to introduce cumbersome mathematical manipulation in the attempt to derive the response. It is shown that if one properly distinguishes between the two domains, the response can be derived straightforwardly without the necessity for imposing assumptions relating to the nature of the response. The impulse-response functions relating to a membrane to which are attached an infinite set of periodic line and an infinite set of periodic point impedances, respectively, are derived as examples. The extension of the derivation to other forms of structural systems (e.g., a plate) is straightforward.
Dynamic Response of Suspended Underwater Systems
Authors: Iwan W. D.
Published: October 2005

A method is presented [or analyzing the steady-state or stationary random heave response of suspended underwater systems. The nonlinear continuous system is replaced by a discretized pseudolinear system by means of an equation difference minimization technique. The resulting pseudolinear system is solved by an iterative scheme. An example of the application of the proposed method of analysis to a suspended hydrophone system is given. The example shows that the nonlinear pressure drag forces have a very significant effect on the over-all response of the system. The nature of the response is discussed and some practical conclusions are given.
Acoustically Induced Vibration of Periodically Supported Beams
Authors: Bailey J. R. , Fahy F. J.
Published: October 2005

The acoustic response of a structure can be calculated if the radiation resistance of the structure is known. Unfortunately an exact solution of the wave equation is extremely difficult with the boundary conditions imposed by the mode shapes of periodically supported beams. Approximate solutions are obtained in this paper by defining an effective structural wavelength for sound radiation. The results show that the acoustic response of periodically supported beams is highly dependent on frequency and on the ratio of structural to acoustic wavelength. Consequently, it is shown that adding supports can actually increase the acoustic response. An experimental program is also reported. The sound power radiated from three periodically supported beams and the resonant response of the beams to pure-tone acoustic excitation are measured in a reverberation chamber. The experimental results agree well with the theoretical predictions. [Research sponsored by the Atomic Energy Department of Babcock and Wilcox (Operations), Limited, Great Britain.]
Dynamic Behavior of the Hyoid Bone, Mandible, Tongue, and Thyroid Cartilage During Speech Production
Authors: Waikin K. L. , Abbs J. H.
Published: October 2005

Using lateral-view cinettuorographic techniques, movement activities of the hyoid bone, mandible, tongue, and thyroid cartilage were observed. The speakers read 18 CVCV nonsense utterances imbedded in a carrier phrase. A stressed-unstressed/unstressed-stressed paradigm was employed within this disyllable utterance. Using a computerized frame-by-frame analysis technique [provided by the Speech Communications Research Laboratory, Inc., Santa Barbara, Calif.], movement characteristics were retrieved separately for the vertical and horizontal displacement components of each structure. From the retrieved data separate linear displacement plots for each structural component were produced as a function of time. The relations among simultaneous movements of the mandible, tongue, thyroid cartilage, and hyoid bone during productions of the vowels /i, a, u/ are reported as a function of adjacent consonant and syllable stress.
Variations in Mandibular Displacement, Velocity, and Acceleration as a Function of Phonetic Context
Authors: Abbs J. H. , Netsell R. , Hixon T. J.
Published: October 2005

Continuous displacement, velocity, and acceleration of the mandible were recorded along with intraoral air pressure and audio to provide some initial data on mandibular dynamics as a function of place of articulation (p, t, k) and vowel height (i, æ). The muscle-forcing-function interpretation of acceleration, reported at the last meeting of this society by the present investigators, is incorporated. Relative timing between airstream valving, glottal onset-offset, and mandibular activity provides some basic data on patterns of system coordination as they vary with phonetic context. These results also provide some additional information on the coupling between the mandibular and lingual movement systems for speech.
An Electromyographic Investigation of the Feature of Tension in Some American English Vowels
Authors: Raphael Lawrence J. , Lehman Herbert H.
Published: October 2005

Both the traditional vowel triangle and more recent schemes of vowel classification present us with a picture in which the members of at least three pairs of vowels, /i-I/, /e-ɛ/, and u-U/, are said to be differentiated from each other by a feature of tenseness. It has been suggested that differences in tension between the members of a tense-lax pair of vowels are manifested in the extrinsic muscles of the tongue. In the experiment reported here, electromyographic potentials for the genioglossus muscle were investigated to determine the extent, if any, of tension differences between the members of the pairs of vowels listed above. It was found that the posited differences in tension do exist, although the findings cast some doubt on traditionally proposed height relationships for the front series of vowels, /i-I-e-ɛ/. Electromyographic potentials of muscles associated with jaw opening and tongue backing were investigated to see if the genioglossus data could be reconciled with the usual height ordering of the front vowels. Results indicate that there is reason to believe the height ordering of these vowels generally presented in the literature is correct.
Oral and Nasal Sound Pressure Levels as Related to Hyponasality
Authors: Massengill Raymond
Published: October 2005

A number of studies have been conducted concerning the oral and nasal sound pressure level for individuals judged to be hypernasal. Many of these studies have also dealt with whether the subject lacked or obtained complete velopharyngeal closure. Limited research has been conducted concerning oral and nasal sound pressure levels for individuals judged to be hyponasal. In the present study a probe-tube microphone arrangement using a graphic level recorder was employed to study the oral and nasal sound pressure levels for patients judged to be hyponasal. The patients in this study were all judged to have rather large tonsils and none had undergone a complete adenoidectomy. The results of this study are reviewed as well as indications for additional research.
Intraoral Air Pressures Associated with Stop Consonants in Various Phonetic Environments
Authors: Ruder Kenneth F. , Brown W. S.
Published: October 2005

Previous research has demonstrated that intraoral air pressures associated with stop consonants vary as a function of the contextual environment of the consonant (initial, medial, or final syllable position). In the present study, the effect of adjacent phonemes on the intraoral air pressures for the stop consonants /p/, /b/, /t/, and /d/ was investigated. Recordings of peak intraoral air pressures were obtained from five subjects for each of the four stop consonants in the environment of high front vowels, low front vowels, high back vowels, low back vowels, and other consonants. Highest intraoral air pressures were associated with the stop consonants in the consonant environment; the next highest pressures were associated with the high vowel environment while the lowest pressures occurred in the low vowel environment. No differences in intraoral pressures for the four stop consonants were observed in comparison of the front and back vowel environments. These findings can be interpreted as reflecting a co-articulation effect and thereby demonstrate that phonetic environment does affect the magnitude of the intraoral air pressures associated with stop consonants. The data from the present study also support the trend reported in previous studies for higher intraoral pressures to be associated with voiceless consonants.
Midsagittal Displacement Patterns of Points on the Tongue Body During VCV Utterances
Authors: Kent R. D. , Moll K. L.
Published: October 2005

The object of this study was to characterize the movements of the tongue body during consonant articulations by the displacement patterns of individual flesh points. Radiopaque markers were placed on the tongue body, and the displacement patterns of these markers during symmetric VCV utterances were recorded by means of cinefluorography. Two speakers recited utterances that were constructed with the vowels /i,u,a/ and the lingual consonants /g,j,d,z/. Additional data are presented for two other speakers to demonstrate the presence of tongue movement during symmetric VCV utterances in which the intervocalic consonant is the nonlingual fricative /v/. The discussion includes comments on consonant-vowel interaction, remarks on certain peculiarities of the tongue-point movements, and some speculations as to active and passive forces during lingual articulation. [Research supported in part by grants from NIH.]
Cinefluorographic Studies of Selected American English Diphthongs
Authors: Kent R. D. , Moll K. L.
Published: October 2005

The observations reported in this paper pertain to the articulatory movements—especially tongue movements—that are associated with the American English diphthongs /al/, /ɔI/, and /aU/. Flesh points on the lingual surface were simulated by attaching small radiopaque markers to the midline of the tongue body. Lateral-view cinefluorography was used to record the displacement patterns of these markers during the production of diphthongs in isolated words and short sentences. Data were collected for three speech samples, each of which was read by a different set of two speakers. Consideration of these data emphasizes the general problem of identifying invariant phonemic correlates at the articulatory level, with illustrations of the variability in (1) the initial and terminal vocal-tract configurations for a given diphthong, (2) the patterns of tongue-point movement for a given diphthong, and (3) the tongue-point velocities during a given diphthong. [Research supported in part by grants from NIH.]
Responses of High-Frequency Inferior Colliculus Neurons to Interaural Intensity Disparities
Authors: Stillman Robert D.
Published: October 2005

Most high-frequency binaural neurons in the inferior colliculus of the kangaroo rat discharge at a higher rate when the contralateral stimulus intensity exceeds the ipsilateral. Since low-frequency inferior colliculus neurons are usually most responsive to contralateral time leads, the present results support the position that this midbrain nucleus transmits information primarily concerning sounds originating in the contralateral field. The binaural response of high-frequency neurons most often reflects the interaction of a contralateral excitatory and an ipsilateral inhibitory input. Some responses, however, indicate the presence of complex bilateral neural interactions. For example, one particular group of neurons discharges maximally at specific interaural intensity differences independent of frequency and over-all level. Such neurons possess a “characteristic intensity difference.” Other neurons shift their discharge rate, temporal discharge pattern, or response latency with changes in the interaural intensity. All of these neurons, therefore, are sensitive to the stimulus parameter which is responsible for the ability to localize high-frequency sounds. [Supported by NINDS Postdoctoral Fellowship and NIH Grant to G. Moushegian.]
Cochlear Nucleus Intracellular Study of Responses to Steady-State and Frequency-Modulated Stimuli
Authors: Britt Richard , Starr Arnold
Published: October 2005

We have studied a total of 164 cochlear nucleus cells and 22 eighth nerve fibers in 46 pentobarbital anesthetized cats. Tuning curves, peristimulus time histograms, and responses to triangular frequency-modulated sweeps were made. Eighth nerve fibers have a characteristic PSTH characterized by gradual adaptation. Responses to FM signals were symmetrical over the intensity and sweep rates tested although firing was enhanced with faster modulation rates. The same type of PSTH and FM responses were seen in many cells in the ventral cochlear nucleus and only occasionally in the dorsal cochlear nucleus (DCN). Many units in the dorsal cochlear nucleus show, instead, complex response patterns to both steady state and FM signals. Some DCN units which have a symmetrical response to FM signals at high intensities show asymmetry or directionality as signal strength is lowered. Units with only an onset response to tone burst or showing nonmonotonic intensity functions were likely to show asymmetry or directionality in their FM response. Both the discharge data and the membrane potential shifts suggest that the ventral cochlear nucleus acts as a relay station transmitting information coded at the periphery. The dorsal cochlear nucleus, however, seems to have an active role in extracting and recoding information. [Supported by NINDS and Giannini Foundation.]
Relation of the Lateral Inhibition in the Auditory System to the Critical Bandwidth
Authors: Ujihara Jun-ichi , Sakai Hisao
Published: October 2005

The auditory peripheral system is simulated in terms of an electronic model and the critical band is discussed to relate to the inhibitory area. The electronic model consists of the basilar membrane, hair cells, and the primary and secondary neurons. Each neuron has lateral connections so as to have a response area and inhibitory areas observed in the physiological experiments. When two tones are applied to the model simultaneously, a spatial response pattern along the neurons is either single peaked or double peaked, according to whether or not the frequency interval of two tones is less than the frequency difference between the best frequency and the inhibitory characteristic frequency. On the other hand, the relation between the masking patterns of two components tone were previously discussed by J. J. Zwislocki [Handbook of Mathematical Psychology (Wiley, New York, 1965) Vol. 3, p. 77]. On the assumption that the spatial response pattern of neurons closely corresponds to the masking pattern, it is derived that the frequency interval between the best frequency and the inhibitory characteristic frequency agrees with the critical bandwidth.
Digital Simulation Model of the Basilar Membrane
Authors: Lovell John D. , Carterette Edward C. , Nagel David C.
Published: October 2005

A new model and digital simulation program for basilar membrane motion is presented with several improvements over previous models. The model attempts to account for both earlier data (e.g., those of von Békésy) and more recent data [e.g., those of Rhode, J. Acoust. Soc. Amer. (to be published)] relative to basilar membrane dynamics. The model consists of a mixed linear and nonlinear part and represents the basilar membrane as a lumped parameter system. The nonlinear scaling factor and time delays were omitted from Flanagan's original model. Travelling-wave envelopes or instantaneous positions may be displayed for any arbitrary signals input to the membrane. The new model also has sharper tuning for single membrane sections and an 8-φ phase lag range. Details of the digital computer programs will be given and a range of applications of the model suggested. [Work supported by the United States Public Health Service, under Grant MH-7809.]
Modulation Index as a Response Criterion for Discharge Activity
Authors: Littlefield Warren M. , Pfeiffer, Russell R. , Molnar Charles E.
Published: October 2005

The fact that spike discharges of spontaneously active cochlear nerve fibers demonstrate phase locking in response to low-frequency sinusoidal stimuli at signal levels substantially lower than those required to generate a change in spike discharge rate has led us to investigate the properties of the following response criterion. We evaluate the index of modulation of the spike discharge rate as a result of the sinusoidal stimulus. Period histograms are modelled as an inhomogeneous Poisson process. Using maximum likelihood techniques, we estimate the index of modulation and the phase difference between the stimulus and the response. We have acquired data similar to “tuning curves” showing as a function of frequency the stimulus level necessary to maintain an arbitrary fixed level of modulation along with the corresponding stimulus-response phase relations for the complete response-band of fibers with low CF (<3 kHz), and for low-frequency portions of the response-band of fibers with high CF (>3 kHz). We compare these results to those obtained using other response criteria, and examine their relationship to cochlear mechanics and cochlear microphonics. [This investigation was supported by PHS research grants from the National Institutes of Health.]
Measured Noise of Model Jet Flap Systems for Lift Augmentation
Authors: Groeneweg John F. , Minner Gene L.
Published: October 2005

Noise measurements were made on two jet flap systems proposed for STOL aircraft. In one case a 6-in.-diam fan was mounted under the wind such that the exhaust impinged on downwardly deflected flap segments. In the other case, the fan was located on the upper surface of the flap such that fan and flap moved as a unit, with no exhaust impingement. Results for take-off and approach fan speeds and flap deflections were used to estimate STOL airplane perceived noise levels. Internally generated noise directivity corresponded with fan axis orientation for the fan-on-flap, but no consistent redirection of internal noise was observed with changes in flap angle for the fan-underwing. With the fan-on-flap arrangement, the wing shielded some fan inlet noise from the ground. Since no impingement of the exhaust on solid surface occurred, the external noise was jet noise alone. In contrast for the fan-under-wing, the jet/flap interaction noise dominated the external noise even with no flap deflection. If internal noise is reduced by fan design and acoustic treatment, the jet/flap interaction noise will dominate. Additional work is needed to establish a spectral correlation of interaction noise.
Measured Discrimination of Boundary-Layer Pressure Fluctuations by Round, Square, and Rectangular Transducers
Authors: Recine E. C.
Published: October 2005

Pressure fluctuations obtained in a turbulent air pipe flow facility were measured using 19 flush-mounted transducers that varied in size and shape. The results of these measurements, in the form of spectral density. were then compared with the results obtained using a modified theory on transducer size correction originally proposed by Corcos. The modification, introduced by White, consisted of using the measured transducer response kernel. Agreement between the experimental data and theoretical predictions was good. In the midfrequency range, transducers that had their longest dimension parallel to the flow produced the greatest discrimination against pressure fluctuations. At high frequencies, the response becomes a function of size and independent of shape, as predicted.
Low-Wavenumber Component of Turbulent Boundary Layer Pressure Fluctuations
Authors: Jameson P. W.
Published: October 2005

Measurements of the modal vibration of a thin steel plate excited by turbulent boundary layer pressure fluctuations in air are described. This vibration is believed to be caused by Fourier components of the turbulent pressure that have the same phase speed as bending waves in the plate, a speed which is subsonic but much higher than the flow speed. The measured vibration is used to infer the wavenumber spectrum of the turbulent boundary layer pressure.
Spatial and Spectral Dependence of Noise Power in the Ocean
Authors: Anderson Victor C.
Published: October 2005

Background noise measurements were conducted from the Research Platform FLIP using a 31-element DIMUS array. The data consist of sampled sequences of the detected beam outputs of the DIMUS beamformer. The data have been processed with an FFT computer program to yield fluctuation power spectra along both the time coordinate and the bearing coordinate. The spatial spectra indicate that the sources of fluctuation have a higher frequency content relative to the Knudsen curves. The temporal envelope spectra show a strong negative frequency slope in the region 0.01–10 Hz, in variance with the commonly accepted Gaussian model.
Acoustic Wave Scattering at Randomly Rough Surface: A Computer Simulation
Authors: Caruthers Jerald W. , Novarini Jorge C.
Published: October 2005

A technique for studying wave scattering from a randomly rough surface by computer simulation has been developed. Surfaces having desired directional spectra were simulated using two-dimensional filter theory. Scattering was simulated by forming facets in the surface and applying the laws of reflection at each facet and accumulating the rays, with due consideration of phase and spreading, on a receiver grid. Wind-driven sea surfaces having Neumann-Pierson and Pierson-Moskowitz spectra for several wind speeds were formed. These surfaces were tested through the autocovariance functions and variances. A close agreement with the expected behavior was found. Preliminary scattering results for a Neumann surface having a wind speed of 5 msec−1 in terms of coherent and incoherent parts of the intensity, pressure, amplitude and phase fluctuations, and spatial correlations are reported. Also, a study of the distribution of total intensity as scattered from a SWOP surface is reported.
Covariance Function of the Acoustic Backscatter from a School of Fish
Authors: Swarts R. L.
Published: October 2005

A recently developed statistical model for first-order scattered fields is used to predict the normalized covariance function of an underwater acoustic signal backscattered by a hypothetical school of fish. The fish school is configured as an oblate spheroid with the individual fish Poisson distributed within the school. Empirical covariance functions are determined using ensemble averaging techniques from experimental data obtained by insonifying an actual school of fish with gated 28.2-kHz continuous-tone signals. A comparison of theory with the experimental results is made.
Underwater Sound Reflections from Some Seamounts Off the California Coast
Authors: Northrop John , Wheeler R. B.
Published: October 2005

During the last week in June 1970, recordings of underwater sound reflected from some seamounts off the California coast were obtained with a directional 1.5-kHz source pulsed in the CW, FM, and PRN modes from a submerged submarine at 200-ft depth near 33°N, 121°W. Pulses were from 12 to 5 sec long at a nominal source level of 135 dB re 1 μbar at 1 yd. An on-board computer (in addition to a strip chart recorder) was used to record signal level versus time at 110-sec intervals for as long as 200 sec after the outgoing pulse. The sound-speed profile consisted of a weak surface channel at 100 ft and a deep-sound channel at 2950 ft (axis depth). Water depths between source and seamount were sufficient (∼2000 fm) for convergence-zone propagation. Seamounts encountered ranged from 1000 to 1700 fm in depth (minimum sounding) and were from 10 to 30 miles wide at the base. Reflections from seamounts at ranges of up to 75 miles were recorded on some of the five discrete azimuths probed. Signal levels near 20 dB above background were observed for reflections from some of the seamounts. The levels were higher for seamounts situated between convergence zones as well as for the larger and shallower mounts.
Covariance Functions and Associated Statistics of Acoustic Scattering from Lake Surfaces
Authors: Plemons T. D. , Shooter J. A. , Middleton D.
Published: October 2005

A statistical analysis using ensemble averages is made of reverberation data obtained from the wind-driven surface of a fresh water lake. To produce the reverberation, gated CW pulses are transmitted to ensonify the scattering surface. The center frequency of each transmitted signal is 110 kHz. Two pulse durations, of 0.1 and 1.0 msec, are used in the CW experiment. The transmitter and receiver are located at essentially the same place (R@T); i.e., the operation is monostatic. The grazing angle is 22°. Particular care is taken to ensure that a valid ensemble is obtained. Thus, the analog time functions which represent the reverberation process are recorded on magnetic tape and converted to digital samples which are sorted into the sample ensembles. The validation (or invalidation) of these data consists of testing each sample ensemble for independence (a one-sample-runs test) and homogeneity (a Kolmogorov-Smirnov test). From sample ensembles that prove to be valid, various second-order statistics of the reverberation are estimated. Presented here are the two-dimensional covariance functions which reveal through their asymmetry the nonstationarity of the reverberation. In a companion paper, J. A. Shooter discusses the co-intensity spectra of these data. [This work was performed under contract with Naval Ship Systems Command.]
Asymmetry of Spectra of Surface Reverberation in Shallow Water Propagation
Authors: Brooks David A. , DeFerrari Harry A.
Published: October 2005

Acoustic energy when striking a moving sea surface is both frequency-shifted and scattered. If the surface is periodic, scattering will occur in preferred directions governed by Bragg's law of diffraction. The frequency associated with each scattered direction will differ by an integer multiple of surface frequency from that of the insonifying source. Scattering theory predicts symmetry in frequency and amplitude of the scattered energy. The former has been experimentally verified (Roderick), but amplitude asymmetry is frequently observed in scattering experiments. At the Miami acoustic range, energy diffracted toward the normal (downscatter) is consistently stronger at the 7-mile hydrophone than energy diffracted away from the normal (upscatter). Computer models of a two-layer free-surface acoustic waveguide were developed and investigated to determine the causes of scattering asymmetry. Model results indicate that amplitude asymmetry is a result of the Bragg scattering geometry. In shallow water, a range-sensitive downscattered preference for a bottom-mounted receiver is predicted in agreement with observation. In deep water there may be ranges at which upscattered energy will be the stronger.
Average Mechanical Impedance for Random Vibration
Authors: Noiseux D. U.
Published: October 2005

The response of a system to a random stationary process applied at selected points of a mechanical structure is readily formulated in terms of the mechanical impedance matrix of these points. However, in practice the results suffer from many uncertainties: uncertainties in the measurements of the mechanical impedances; uncertainties in the boundary conditions of the subsystems; uncertainties in the power spectral densities of the excitation itself. These uncertainties are reviewed. The propagation of the uncertainties in the calculations lead to errors which grow rapidly with the complexity of the calculations. At the other extreme, simplified but approximate calculations using average (over frequency bands) impedances lead to errors which do not grow as rapidly because the dynamic range of average impedances is much smaller than the dynamic range of true impedances, and because the calculation format is simpler. The simplified measurements of, and calculations with, average impedances may be used either as a practical criterion for determining where the classical calculations break down, or as a practical compromise in the estimates of the response.
Determination of Machinery Foundation Vibration Transmission with Impedance Techniques Applied to Plastic Models
Authors: Bannister Ronald L.
Published: October 2005

Scale plastic models with terminations of known impedance have been used in the laboratory to understand and control the vibration transmission of machinery foundations. Experimental results show that these models can be used to determine (1) natural frequencies, (2) average response levels, and (3) mode shapes. Use of the mechanical impedance technique has made it possible to determine the variation of machinery foundation vibration transmission as a function of (1) impedance matching, (2) stiffening, (3) drive force location, and (4) phasing of multiple input forces. This paper reviews the progress of scale plastic model work-scaling laws, material characteristics, impedance analyses, experimental procedures, and test instrumentation. Experimental model and prototype studies are reviewed to illustrate the potential of using scale models in the laboratory to investigate the dynamic behavior of complex structural configurations.
A Cross-Language Study of Perceptual Asymmetry
Authors: Myers T. F. , Wolf J. J.
Published: October 2005

Recent findings that the speechdominant hemisphere is specialized at the level of distinctive feature analysis entail a prediction that the processing of acoustic cues embodying a feature distinction in a particular language is asymmetric for “native” listeners, but not asymmetric for nonspeakers of the language if their own language does not employ the contrast. Russian- and English-speaking listeners were presented dichotic sequences of syllables for identification of the consonants, i.e., the stops, categorized in Russian, but not in English, as palatalized or nonpalatalized. The results are discussed in the context of a recognition model equipped with a “filter” for feature selection.
A Search for the Perceptual Features of the 29 Prevocalic Hindi Consonants
Authors: Singh Sadanand , Singh Kala
Published: October 2005

The 29 consonants of Hindi were recorded prevocalically with the vowel /ʌ/. Each consonant was included in proportion to its statistical probability in Hindi. Thus, while /p/ was included five times, /k/ 14 times. Ten native speakers of Hindi listened the stimuli in each ear separately in five S/N ratio conditions. Listeners responded in an openchoice manner. The responses were written in Devnāgri script. The tallies were made for all the errors which were then averaged for each stimulus consonant across the 10 subjects. The analysis of the 10 matrices (five S/N ratio × Ears) by IND-SCAL method provided beat interpretation in fivedimensional space. The perceptual features obtained were best described in articulatory terms. The first two dimensions were interpreted as voicing, aspiration, and sonarant with further interpretation of sonarant as: retroflection, nasality, laterality, and semivowel. A subset of 22 consonants, for which place of articulation was phonogically distinctive, was further analyzed. The analysis yielded perceptual features (with articulatory nomenclature) front/back and palatal. [This work was partially supported by a grant from NIH.]
Perception of Segments of Spoken (Hindi) VowelConsonant-Vowel Syllables
Authors: Agrawal S. S. , Gupta S. K. , Ahmed Rais
Published: October 2005

This study presents some results of an experiment conducted to determine the effect on perception of deleting different numbers of 10-msec segments from the initial and final parts of VCV syllables. Eight stop consonants /p,t,t,k,b,d,d,g/ and two affricates /ts,dz/ were combined with three pure vowels /i,a,u/ to produce 30 VCV stimulus words. An electronic gating apparatus was developed to present sequential segments of initial and final portions of these syllables. The VC and CV stimuli so obtained were used for two separate listening tests and the responses were analyzed for individual consonants as a function of time. Perceptual phoneme boundaries were found from the response curves and compared with the acoustical phoneme boundaries obtained from sonagrams. The results indicate that the transitions of initial and final vowels terminating in the consonant are of maximal importance for the recognition of intervocalic consonants. The data indicate that the plosive burst plays a more important part in the recognition of unvoiced stops than in the case of voiced stops. The plosive gap was found to play a greater role in the recognition of voiced stops. The affricates were found to utilize all the acoustic events for their recognition. The study of errors showed that for intervocalic consonants, the voicing feature was not recognized in the early part of the initial transition and in the end part of final transition.
Singular Perturbation Methods in Nonlinear Acoustics
Authors: Crighton D. G.
Published: October 2005

The application of singular perturbation techniques to problems in nonlinear acoustics is demonstrated in two examples. In the first, we show that straightforward perturbation methods, using Lighthill's equation for aerodynamic sound, give a secular series when applied to one-dimensional simple wave flow. The nonuniform secular terms are removed by the introduction of expansions in terms of multiple scaled coordinates, and the Earnshaw solution for the shock-free region is recovered. Such an expansion technique is also applied to solve a problem in compound flow. In the second example, the method of matched asymptotic expansions (MAE) is applied to one-dimensional flow governed by Burgers' equation. If the excitation at the origin is time harmonic, Burgers' equation can be solved exactly, and the solution reduced to an intelligible form in the shock-free, saw-tooth, and saturation regions. These simplified approximate solutions are recovered by a direct application of MAE to Burgers' equation, and in work still under completion, it appears that the same process will yield a uniformly valid approximate solution of the analogous problems in two and three dimensions.
Finite-Amplitude Wave Propagation in Relaxing Fluids
Authors: Klinman R. , Kraus L.
Published: October 2005

The Eulerian equations of motion for wave propagation in a relaxing fluid are transformed to the Lagrangian representation by a Von Mises transformation. A single third-order equation is obtained, which, for certain ranges of the physical parameters (much number, source frequency, dispersion number, and relaxation time), has uniform, i.e., shock-free, perturbation series solutions. The solution to second order exhibits harmonic generation and spatial beat waves due to velocity-dispersion-induced phase shifts. Examination of the inverse transformation yields additional information on the shock behavior of the system. The region in which the Lagrangian and the previously determined Eulerian results [R. Klinman, L. K. Chi, and L. Kraus, J. Acoust. Soc. Amer. 49, 118 (1971)] for relaxing fluids is determined. [Work supported by Office of Naval Research.]
Numerical Calculation of the Nearfield for Spherically Symmetric Nonlinear Acoustic Flows in an Unbounded Ideal Gas
Authors: Muller G. M.
Published: October 2005

An implicit finite-difference method has been developed for calculating spherically symmetric nonlinear acoustic flows generated by a high-intensity periodic source. This method makes it possible to match the conditions prescribed at the source to a low-amplitude solution (in Blackstock's sense) valid at large distances from the source. Numerical computations have been made for pistonlike and sirenlike sources of three different periods and several source amplitudes. Selected graphs of the results will be presented, together with estimates of the errors associated with the method of computation. The numerical results will also be used to show that, in some instances, a low-amplitude solution may be matched directly to a given source even though the conditions for validity of that solution are not satisfied near the source. [Work supported by Aerospace Medical Research Laboratory, Air Force Systems Command.]
Variation in Eighth Nerve AP Waveform as a Function of Age in Rats
Authors: Crowley D. E. , Schramm V. L. , Swain R. E.
Published: October 2005

Analysis of computer-summed click-evoked APs recorded from the round window of rats at ages from 1 to 24 months revealed that: (1) The mean visual detection levels of unaveraged APs rises progressively from 6 to 24 months by 16.5 dB. (2) N1 amplitude rises from 1 to 12 months, and then declines to 24 months at all but the lowest level (50 dB SPL P.E.) as reported at the previous meeting of this society. (3) Conversion of N1 amplitudes to percents of maximum amplitude for each animal eliminates the above age effect, as expected. (4) N2 amplitude increases from 1 to 6 months, but shows only a slight decline to 24 months. (5) The positive peak separating N1 and N2 remains fairly constant between 1 and 12 months and rises sharply to 18 months, followed by a decline to 24 months. For rats from 1 to 18 months, the general effect of increasing click level is to increase the amplitude of this peak, while at 24 months, the peak decreases and becomes negative at 120 dB SPL P.E. (6) N1 latency decreases with click level at all age groups, but does not appear to change with age at any but the lowest click level. (7) The temporal separation between N1 and N2 does show a decrease as a function of advancing age. As a function of click level, N1−N2 separation is slightly reduced at moderate levels, compared with its values for low and high levels. [This research was supported by the Deafness Research Foundation].
Traveling Wave—Source of Negative Summating Potentials
Authors: Prazma J.
Published: October 2005

Cochlear microphonics (CMs), summating potentials (SPs), endocochlear potentials (EPs), and potassium concentration (K+) have been recorded from the guinea pig's cochlea. Standard glass microelectrodes and microelectrodes sensitive for K+ have been introduced into the scala media. In the first part of the experiments, potentials were measured under different sound pressure levels (SPLs)—80, 90, and 100 dB at I, II, and III turns. In the second part of the experiments, changes in K+ concentration, SP, CM, and EP (following anoxia and perfusion of the scala tympani by Ringer's solution, ethacrynic acid, and artificial endolymph) were recorded. Maximum negative summating potentials with their increasing SPL were recorded in loci appropriate for the analysis of those frequencies. Continuous changes in potentials and K+ concentration are produced by anoxia and by ethacrynic acid in the scala tympani. In both experiments, when active ion transport is paralyzed, the concentration of K+ in in the scala media and the negativity of SP falls. Replacement of perilymph in the scala tympani by a solution with the same concentration of K+ as endolymph immediately produces a rapid increase of K+ concentration inside the scala media and at the same time an increase in the negative SP. [Supported by NIH grant.]