bluuebunny/crossref_metadata_2025 huggingface dataset:
Focusing and Refraction of Harmonic Sound and Transient Pulses in Stratified Media
Authors: Sachs D. A. , Silbiger A.
Published: October 2005

In media for which the speed of sound is position dependent, propagating sound will be refracted and, in some cases, focused. In the focusing regions, usually referred to as caustics or convergence zones, significant amplification of the pressure levels above those predicted by spherical spreading has been observed for continuous waves as well as for explosive pulses. In addition, the waveforms of explosive pulses undergo drastic distortion. In the present paper, an asymptotic theory of the refraction and focusing of sound originating from a point source in a stratified medium is presented. It is applicable to realistic velocity profiles and encompasses both transient pulses and harmonic waves. A comparison with Barash's and Goertner's recent experiment involving explosive pulses indicates that the theory gives reliable estimates of the peak pressure levels at caustics, but reproduces only qualitatively the shape of the focused pulse. The discrepancy is attributed mainly to the neglect of finite-amplitude effects in the theory's formulation. The inaccuracies inherent in the high-frequency asymptotic methods employed in the theory are discussed in some detail.
Dual Representation of the Green Function of a Vibrating Finite String
Authors: Tucker A. J. , Maidanik G.
Published: October 2005

The Sommerfeld-Watson transformation is employed to derive the wave representation of the Green function of a vibrating string from its modal representation. The execution of the transformation is not trivial, and it possesses features that may prove useful in attempts to apply it to more complex structural systems.
Scattering of Sound by Underwater Turbulence
Authors: Kaufman Charles
Published: October 2005

The cross section for scattering of sound by underwater turbulence is calculated by modifying Monin's calculation of the same effect in the atmosphere. The contributions of thermal inhomogeneities and flow velocity inhomogeneities are explicitly separated. Using parameters appropriate to relatively intense natural ocean turbulence, it is seen that the temperature variations are the more important cause of the scattering of sound.
Handy Curves for Finding the Source Level of an Explosive Charge Fired at a Depth in the Sea
Authors: Urick R. J.
Published: October 2005

A set of curves is given to facilitate finding the source level of explosive charges fired at any depth in the sea.
Brillouin Scattering from SF6 in the Vicinity of the Critical Point
Authors: Mohr R. , Langley K. H. , Ford N. C.
Published: October 2005

Using techniques described by Ford, Langley, and Puglielli, we have observed Brillouin scattering from SF6 near its critical point for two scattering angles, 166° and 45°. Sound velocities deduced from these measurements at T−Tc=0.5°C are Cs=112±1 m/sec for a sound frequency of 370 MHz and Cs=95±2 m/sec for a frequency of 130 MHz. The dispersion in the sound velocity of about 15% at T−Tc=0.5°C decreases as the temperature is increased to about 1% at T−Tc=40°C, where the sound velocity has increased to 160 m/sec. These data are compared with existing ultrasonic data and discussed in the light of a dynamical model considered by Mountain.
Phonon Instabilities and Interactions near Solid-State Phase Transitions
Authors: Fleury Paul A.
Published: October 2005

The recent observation of soft optic modes which trigger structural phase transitions of several different kinds leads naturally to the suggestion that the anomalous acoustic behavior near these phase transitions might arise from interactions between acoustic phonons and the soft optic modes. In this paper we explore this suggestion from both theoretical and experimental points of view. The concept of the soft mode is explained for both phonon and tunneling modes whose instabilities may occur at the center (q=0) or the boundary (q≈π/a) of the Brillouin zone. Illustrative experimental results from infrared absorption, light scattering, and neutron scattering techniques are presented. We review and compare several theories of the interaction between acoustic phonons and soft optic modes and cite appropriate experimental evidence, where available, for comparison. Among the crystals discussed are SrTiO3, KDP, KTaO3, and NH4Cl. We conclude that basically two types of optic-acoustic interactions are sufficient to describe most structure transitions. However, to date, a complete microscopic description in quantitative agreement with experiment, both above and below Tc, has yet to appear. Nevertheless, the explanation of acoustic anomalies in terms of soft optic mode behavior is essentially correct and will prove quite fruitful.
Differences of Interaural Phase and Level in Detection and Lateralization
Authors: Jeffress Lloyd A. , McFadden Dennis
Published: October 2005

By employing the same narrow band of noise (50 Hz wide, centered at 500 Hz) as both masker and signal, and by introducing a phase-shifting network between the masking and signal channels, it is possible to control the phase angle, α, between the two. For a given signal-to-noise ratio, controlling the phase angle, α, controls the relative magnitudes of the interaural phase (time) difference and the interaural difference in level between the stimuli at the two ears. When α lies between 0° and 90° and the signal is reversed at one ear relative to the other (N0Sπ), the interaural time difference and the interaural level difference favor the same ear. However, when α is between 90° and 180°, the ear that leads in phase or time will receive the weaker stimulus, thus putting time and intensity into opposition as cues to the lateralization of the stimulus. Data on both detection and lateralization were obtained using the single-interval forced-choice procedure. Large masking-level differences were found at all values of α, and good detection was exhibited even at those values of α where time and intensity were in opposition, and where performance in lateralization was very poor. Substantial individual differences in the relative importance of time and intensity as cues were found among the subjects.
Lateralization and Detection of Noise-Masked Tones of Different Durations
Authors: McFadden Dennis , Pulliam Kenneth A.
Published: October 2005

On different blocks of trials, subjects were asked either to detect or to lateralize a monaurally presented signal (Sm) in a binaurally presented noise masker (NO). Eight values of signal duration, ranging from 50 to 800 msec, were used for both detection and lateralization. The psychometric functions for lateralization and those for detection differed in form, but, despite this difference, both were displaced toward greater signal levels at about the same rate as signal duration decreased. That is, the difference between lateralization and detection was approximately the same for all signal durations. Signal: 400 cps. Masker: wide-band noise, 45 dB SPL/cycle. Method: single-interval forced choice.
An On-Line Recognition System for Spoken Digits
Authors: von Keller T. G.
Published: October 2005

A digit recognition system based on simple segmentation rules according to articulatory features is described. The digits are segmented according to manner of articulation, and the first two formants are automatically tracked for vowel-like segments. Each digit is represented by a sequence of segments and five formant values, namely, the first and second formant at the beginning and the end of the segment and the maximum value of the first formant within the segment. Reference patterns are established and unknown utterances are matched against them. Error rates range from 1.2% to 5.0%, and reject rates range from 1.1% to 4.4% for different experiments.
Auditory Masking of One Pure Tone by Another in the Bottlenosed Porpoise
Authors: Johnson C. Scott
Published: October 2005

Pure-tone masking-tone thresholds were obtained for a bottlenosed porpoise The masking-tone frequency was 70 kHz. Two masking levels were used, 40 and 80 dB above threshold. The shapes of the masking curves were very similar to those obtained from human subjects at much lower frequencies.
Improvement of Low-Frequency Response in Small Loudspeaker Systems by Means of the Stabilized Negative-Spring Principle
Authors: Matzuk Terrance
Published: October 2005

As a practicable means for extending the low-frequency response of small loudspeaker systems, schemes employing stabilized passive negative springs have been investigated. Experimental loudspeaker systems have been constructed and are described. A typical negative-spring loudspeaker system, consisting of a 4.3-in.-diam diaphragm in a sealed enclosure of 0.105 ft3 provides a piston displacement of 0.200 in. peak-to-peak at 65 Hz, when driven by an input power of 2.3 W into a nominal voice-coil impedance of 11 Ω.
High-Frequency Response of a Point-Excited Cylindrical Shell
Authors: Feit David
Published: October 2005

The normal-mode solution for the response of a point-excited cylindrical shell converges poorly for high frequencies. Converting the normal-mode series to an integral representation using a Watson transformation, we obtain a new alternate representation of the solution which converges with only very few terms in the high-frequency regime. Furthermore, this new representation, when compared to the response of a point-excited plate, can be interpreted as a superposition of propagating disturbances that circumnavigate the cylinder in helical paths from the drive path to the field point, with the phase velocity characteristic of flexural waves in a flat plate.
Scattering of Waves by a Lossy Convex Object with a Statistically Corrugated Surface
Authors: Chen Y. M. , Fan W.
Published: October 2005

The scattering of time-harmonic spherical scalar waves by a large, convex, and lossy object with a statistically corrugated surface is considered. The maximum deviation of the corrugated surface from the smooth one is assumed to be small, and hence the boundary-perturbation technique is used in this study. First, the scattering of scalar waves by a large lossy sphere with statistical surface irregularities is treated as a canonical problem in the general discussion. After the effective reflection coefficient is derived for the sphere case, the asymptotic expressions of mean values of the scattered wave function and the scattered intensity are obtained for the general problem.
Forced Motion of a Viscoelastic Solid
Authors: Robertson Struan R. , Thomas Charles R.
Published: October 2005

The formulation of a general solution to the forced motion of a linear viscoelastic body having a constant Poisson's ratio with a time-dependent body force, a time-dependent traction on part of the boundary, a time-dependent displacement on the remainder of the boundary, and nonzero initial conditions is given.
Higher Powers of Pattern Functions—A Beam-Pattern Synthesis Technique
Authors: Thompson William
Published: October 2005

The expression that results from raising the pattern function of a symmetric linear array of equispaced point sources to some integer power greater than unity can be identified as the pattern function of a larger symmetric linear array of point sources with the same spacing. In this manner, one may determine a distribution of source strengths for a large array so that its pattern displays characteristic features of a smaller array, such as fewer sidelobes. In the case where the original pattern function is raised to an even power, the sidelobes of the pattern of the associated larger array all have the same phase.
Sound-Pressure Distribution and Cavity Resonances for a New Artificial Voice
Authors: Tarnow Viggo
Published: October 2005

The artificial voice studied is the new model from Brüel & Kjær. The acoustic pressure obtained from it is given both in the far- and the nearfield. The pressure distribution in the latter case is compared with the one for the human voice; it is shown that they are similar. When telephone transmitters are tested, the question of the shift of acoustic flux due to reflection of sound waves from the transmitter arises. A measurement of this shift is given. The sound pressure varies with frequency because of cavity resonances in the air volumes within the voice. These resonances are studied by an expansion using eigenfunctions to compute the sound pressure in the volumes. From this follows a way to eliminate a standing wave that causes a disturbingly low sound pressure in a certain frequency range.
Correspondence between Cochlear Microphonic Sensitivity and Behavioral Threshold in the Cat
Authors: Price G. Richard
Published: October 2005

Previously published comparisons between behaviorally measured auditory thresholds and cochlear microphonic (CM) sensitivity have not revealed a close correspondence between the two measures. In this study, behavioral data for the cat from Miller, Watson, and Covell (1963) were compared with CM sensitivity for 30 cats. When the data were corrected to account for the altered resonance of the open bulla and the sound-pressure transformation of the head and auditory meatus of the cat, the two curves were nearly identical in shape. Behavioral threshold, from 0.1 to 20 kHz, is approximately equal to that sound pressure necessary to produce a 0.02-μV CM output at the round window.
Power Flow between Two Coupled Beams
Authors: Davies Huw G.
Published: October 2005

An exact result is obtained for the spectral density of power flow between two beams coupled by a rotational spring of arbitrary strength. It is shown that, by averaging this result over narrow bands of frequency and by suitably defining a modal coupled energy, the basic power-flow energy-difference result of statistical energy analysis can be recovered.
Identification of Place of Consonant Articulation from Vowel Formant Transitions
Authors: Sharf Donald J. , Hemeyer Thomas
Published: October 2005

The study was done to determine the importance of CV and VC formant transitions in the identification of place of consonant production. Syllables made up from consonants (/p,t,k,b,d,g,f,s,∫,v,z,ȝ/) and the /ə/ vowel were recorded and spliced so that the noise portions were eliminated from the CV and VC formant transitions. Seventeen undergraduate students were asked to identify the formant transitions as labial, alveolor, palatal, or no consonant. Analysis of the results indicated that: (1) the number of correct identifications was considerably greater than chance for all sounds except voiceless stops; (2) there were significantly more correct identifications made of VC than of CV formant transitions; (3) there were no significant differences between fricatives and stops; (4) there were significantly more correct identifications of voiced than of voiceless consonants; and (5) there was significant variation related to place of consonant articulation. The best explanation for the findings related to CV vs VC formant transitions appeared to be that elimination of the noise from the transitions reduced the span of the articulatory movements included in the CV formant transition so that it was less sufficient than the VC formant transition for consonant identification.
Hyperbaric Chamber Noise during a Dive to 100 ft
Authors: Murry Thomas
Published: October 2005

In this experiment, sound-pressure levels of the noise in a diving chamber, which was pressurized to a depth equal to 100 ft of sea water, were measured. In the first of two dives, measurements were taken during compression and decompression with a piezoelectric microphone oriented so that it was approximately in a horizontal line with the diver's ear and facing away from the vent. In the second dive, the microphone was at the same position in the chamber, but hanging downward at the diver's ear level. The microphone was previously calibrated under pressure using a reciprocity calibration technique. Measurements were taken with an octave-band noise analyzer located outside the chamber. The results indicate that the noise levels were highest in the frequency range between 300 and 4800 Hz. Hyperbaric noise levels are discussed in relationship to recently proposed damage risk criteria for exposure to noise.
Improved Earphone Enclosure for Communication in Noise
Authors: Bauer Benjamin B. , DiMattia Alfred L.
Published: October 2005

Earphone enclosures are described which embody an improved acoustical network for enhanced noise reduction and efficient performance for an earphone. The network uses two chambers, one adjacent to the ear and the other contained in a reentrant expanded portion of the enclosure. The two chambers are connected by parallel passages, one defining predominantly a resistance and the other an inertance. It is shown that this form of network is more effective than an arrangement of inertance and resistance in series. Cushions filled with nonfluid gel provide high wall impedance for improved noise attenuation and conformance with circumaural contours of the head. Values of noise attenuation are given, measured by artificial head and psychoacoustic methods. Performance of a typical earphone in the enclosure is shown.
Bragg Diffraction Sampling of a Sound Field
Authors: Korpel A. , Kessler W. , Ahmed M.
Published: October 2005

In this paper we describe a novel method of probing a sound field in three dimensions with a focused light beam. In our method, the spatial-temporal modulation impressed upon the light by the sound is extracted by the use of either polarization sensitive elements or spatial filters placed in front of a photodiode. The technique is inherently capable of high-resolution sampling because, as is shown, phase and amplitude of the resulting rf current are indicative of the complex sound pressure in a narrow region around the focus of the light beam. This is in contrast to earlier methods using a narrow collimated light beam which only give an indication of sound-pressure amplitude and phase integrated over the entire width of the sound field traversed by the light beam. The first part of the paper analyzes the mode of operation and discusses sensitivity and resolution in a heuristic manner. The second part provides experimental results for various frequencies and sound media. The third part treats the rigorous theory.
Propagation of Sinusoidal Small-Amplitude Waves in a Deformed Viscoelastic Solid. II
Authors: Hayes M. A. , Rivlin R. S.
Published: October 2005

The mean energy flux vector for a plane sinusoidal wave of small amplitude propagating in an isotropic viscoelastic material subjected to an initial static pure homogeneous deformation is calculated. The results are applied to the study of the internal reflection of an SH wave at the plane surface of a half-space of such material. They are also applied to the reflection-refraction problem at the plane interface between two half-spaces of such materials, subjected to different pure homogeneous deformations.
Adaptive Nonlinear Optimization of the Signal-to-Noise Ratio of an Array Subject to a Constraint
Authors: Winkler Leonard P. , Schwartz Mischa
Published: October 2005

We investigate a stochastic projected gradient algorithm, which can be used to find a constrained optimum point for a concave or convex objective function subject to nonlinear constraints which form a connected region, even when we do not have the objective function available, but only have a noisy estimate of the objective function. When the constraint consists of only one linear equation, We prove convergence to the constrained optimum value and bound the rate of convergence of the algorithm to the constrained optimum value. We then apply this algorithm to the nonlinear problem of automatically making an array of detectors form a beam in a desired direction in space when unknown interfering noise is present so as to maximize the signal-to-noise ratio subject to a constraint on the super-gain ratio.
Nonlinear Acoustical Parameters of Piezoelectric Crystals
Authors: Ljamov V. E.
Published: October 2005

The wave equation for elastic waves in piezoelectric crystals is found, including the third-order terms in the expansion of the thermodynamic potential in the strain and electric field. The effective nonlinear parameters for a general crystal are obtained. In the general case these parameters depend on the second-order and third-order coefficients: nonlinear piezoelectric, electrostrictive, and linear electro-optic. These coefficients are considered for piezoelectric and nonpiezoelectric crystals. Some estimates are given of the values of the nonlinear coefficients.
Sound Radiation by Resonances of Free-Free Beams
Authors: Junger M. C.
Published: October 2005

The pressure field of nonuniform, slender, free-free beams of circular cross section is constructed by modeling the beam as a dipole array. Using the orthogonality relation of normal modes, the farfield pressure in a plane normal to the beam axis is shown to be associated with rigid-body translation and, under highly restrictive conditions, viz. local deviations of the effective beam density from the beam's mean density, on elastic, particularly resonant modes.
Reply to “Comments on ‘Farfield of Pulsed Rectangular Acoustic Radiator’” [P. R. Stepanishen, J. Acoust. Soc. Amer. 52, 434–436(L) (1972)]
Authors: Freedman Albert
Published: October 2005

The relationship between the impulse response function approach and the replica pulse approach is clarified.
Multipath Signal Interference in Time-Dependent Propagation Channels
Authors: Clark John G.
Published: October 2005

Formulas previously derived for multipath CW propagation in time-dependent channels are shown to be special cases of corresponding formulas for repreated-pulse propagation. General expressions that relate the CW and repeated-pulse average power outputs in time-dependent channels are derived.
Acoustic Transmission Line: Some Impedance Properties
Authors: Greenspan Martin
Published: October 2005

The imaginary part of the effective density of a fluid or of a viscoelastic material is zero. The contrary notion arises from an inadequate definition of characteristic impedance. The attenuation cannot exceed 2π Np per wavelength.
Doppler Shift of Surface Backscatter
Authors: Swarts R. L.
Published: October 2005

Spectral analyses of underwater backscattered sound are carried out. Measurements are presented showing different Doppler shifts for volume and surface reverberation. Reversal of Doppler polarity is shown for 180° rotation of the underwater sound transducer. The measurements are compared with predictions of a first-order diffraction model for surface reverberation.
Nonlinear Response of a Straight Beam to Narrow-Band Excitation
Authors: Davis William R.
Published: October 2005

The response of a nonlinear oscillator to narrow-band random excitation is investigated experimentally using a straight beam with clamped ends excited by motion of its supporting base. Multivalued or “jump”-type response behavior is observed for a range of excitation levels centered near the first-mode resonant frequency. The time spent in response levels and the magnitudes of the levels are studied and compared with harmonic response. Large peaks in displacement response are seen for excitation centered at the third-order superharmonic frequency.
Detection of Amplitude Distortion in Flute and Clarinet Spectra
Authors: Gabrielsson Alf , Sjögren Håkan
Published: October 2005

Two experiments about detection threshold values for quadratic and cubic amplitude distortion using flute and clarinet spectra are described. Distortion products were generated in an analog computer. Independent variables were spectrum, sound-pressure level, tone onset, and fundamental frequency. A total of 174 subjects were tested. Data were subjected to analysis of variance and interpretations of main effects and interactions are given.
Community Noise Survey of Greater Vancouver
Authors: Price A. J.
Published: October 2005

This paper describes a community noise survey of the Greater Vancouver Regional District, B.C., Canada, which extends over a land area of some 560 square miles. The survey incorporated approximately 100 000 individual noise measurements recorded over a four-month period. The results are compared with published data from previous surveys and indicate that the statistical noise climate found in residentially zoned areas is almost identical in level distribution to that observed by Donley [Sound and Vibration (Feb. 1969)] for the mid-Atlantic states some years earlier. The distribution of noise sources is discussed and compared to some previously published data. Some suggestions for the selection of community noise legislative levels are also made.
MATHEMATICAL DETERMINATION OF DECIBEL-LOUDNESS INDEX, TABLES FOR VARIOUS FREQUENCIES
Authors: Kirchen Calvin J.
Published: October 2005

An analytic procedure is developed to automate the calculation of loudness according to S. S. Stevens' Procedure for Calculating Loudness: Mark VI. Algebraic polynomials are determined that permit the calculation of loudness indices as a function of decibels at a specific frequency. A procedure is given to permit construction of a decibel-loudness index table for any frequency from 25 Hz to 9 kHz.
Influence of Direct-Current Polarization of the Cochlear Partition on the Summating Potentials
Authors: Durrant John D. , Dallos Peter
Published: October 2005

The effects of electrically biasing the cochlear partition on the summating potentials were investigated in guinea pigs. The DIF (DIF = SV − ST) and AVE (2 AVE = SV + ST) SP responses were observed under polarization as well as the cochlear microphonics. These responses were recorded and the cochlear partition was polarized in the first and third turns; a wide range of stimulus parameters was utilized. The negative DIF and positive AVE components exhibited similar qualitative effects of electrical biasing as the (pure tone) CM, but the amount of change induced in the former responses was typically three or more times greater than that seen in the CM. While the DIF+ exhibited the opposite effects of polarization, compared to these responses, the results revealed an underlying relationship between the positive and negative DIF responses. As a rule, positive polarization currents caused the DIF responses to become less positive and more negative while the opposite was true for negative currents. No systematic level-dependent effects of electrical biasing were observed in the behavior of the negative DIF or positive AVE or in the positive DIF, given the complexities of its input-output function (without polarization). The results pertaining to the negative AVE component provided little basis for concrete conclusions concerning the effects of polarization on this component. The findings of this investigation reflect the involvement of electromechanical nonlinearities in the generation of the summating potentials.
Loudness Balances Employing Signals with Unequal Duty Cycles
Authors: Hattler Karl W. , Stokinger Thomas E.
Published: October 2005

The alternate binaural loudness balance technique was employed to investigate the effects of duty cycle (the percentage of time the sound is on) upon the perceived magnitude of 1000-Hz pure-tone signals. The reference signal was fixed in the right ear at 50-dB sound-pressure level (SPL). In the left ear, the comparison signal intensity was adjusted via a Békésy audiometer to yield equal interaural loudnesses. The loudness of interrupted signals increased as the signal duty cycle was increased. A low-duty-cycle comparison signal was consistently judged to be softer than an equally intense high-duty-cycle reference signal. Furthermore, a high-duty-cycle comparison signal was consistently judged louder than a low-duty-cycle reference signal of the same intensity. The greatest interaural loudness disparity was observed for the experimental conditions in which the interaural duty-cycle difference (high duty cycle minus low duty cycle) was 80%. During a substantial number of trials, this relationship between duty cycle and loudness increased in magnitude throughout the 4-min balancing period. Duty-cycle-loudness effects were enhanced when a 400-msec silent interval separated alternating tones. The results of this study may be incorporated to assist in the explanation of the occurrence of the type-V Békésy pattern in clinical audiology. In addition, they lead to questions concerning the interpretation of experiments in which interrupted signals are presented for loudness evaluation such as experiments on loudness adaptation.
Auditory Frequency Discrimination in the Atlantic Bottlenose Dolphin, Tursiops truncatus Montague: A Preliminary Report
Authors: Jacobs David W.
Published: October 2005

Data taken on one Tursiops truncatus are presented for relative difference limens (DLs) in acoustic frequency discrimination. Base frequencies range from 0.9 to 90.0 kHz. The most sensitive frequency discrimination lies in a band between 2.0 and 20.0 kHz. Weber ratios range in value from 0.0028 to 0.0121.
Physical Analysis of Linguistic Vowel Duration
Authors: Jensen Paul J. , Menon K. M. N.
Published: October 2005

This study examined vowel duration in a language (Malayalam of Southern India) whose vowels contrast phonemically in length. A number of acoustic parameters (formant frequency, fundamental frequency, and intensity) concomitant with duration during stimulus production were examined for their potentially contributing effects. Ten CVCV words, differing only with respect to whether the first vowel was short or long, were uttered in a standard frame and later identified by speakers of Malayalam. The average durations of long vowels were approximately twice that of their short vowel counterparts. Analysis of the other acoustic parameters revealed only small and inconsistent differences between the short and long vowel pairs. It was concluded that the linguistic distinction between short and long vowels may reside in the single parameter of duration.
Ultrasonic Diffraction Loss and Phase Change for Broad-Band Pulses
Authors: Papadakis Emmanuel P.
Published: October 2005

The effective diffraction loss and phase change in the field of broad-band transducers is computed in terms of the normalized distance Sc = zλc/a2 at the center frequency of the pulse. Diffraction corrections for attenuation and velocity are explained, and their limitations stated for broad-band pulses. It is shown that the corrections are functions of bandwidth as well as of Sc.
Use of Moiré Fringes in Investigating Surface Wave Propagation in Monolayers of Soluble Polymers
Authors: Scott J. C. , Stephens R. W. B.
Published: October 2005

The moiré fringe wave visualization technique produces instantaneous records of the wave field, from which the propagation characteristics of the surface may be deduced. This is particularly useful for surfaces whose properties are time variant. Although the wave damping properties of the polymer monolayers examined were considerably more complicated than those of monolayers of simpler surface active agents, existing theory was shown to be adequate in explaining the observed effects on the basis of the surface tension and surface dilational elasticity of the monolayer. This agreement of theoretical prediction with observation supports the evidence for the existence of longitudinal surface waves. Using the moiré technique to investigate the time variation of solution-adsorbed monolayers of poly (ethylene oxide) on water, it was found that this polymer produces from solution the same type of stable monolayer as is produced by spreading the material in a monolayer on a pure water substrate.
Bistatic Backscattering of Low-Frequency Underwater Sound from the Ocean Surface
Authors: Brown M. Vertner , Saenger R. Alfred
Published: October 2005

The bistatic scattering strength S(φi,φs) = 10 logs (φi,φs) of the ocean surface has been measured in 12-oct bands over the frequency range 62.5–4000 Hz for a wide range of grazing angles of incidence and scattering, φi and φs. Explosive charges at the bottom of a vertical string of hydrophones were used to ensonify the surface. Concurrent measurements of surface roughness were taken with an accelerometer float. S was obtained for rms waveheights Ĥ between 1.9 and 2.8 ft and rms omnidirectional slopes tanΘ̂ between 0.10 and 0.13. For frequencies between 62.5 and 1440 Hz, the bistatic scattering coefficient s may be represented in the form s=CeD[sinφi+sinφ2]2, where C and D are functions of the surface roughness parameters kĤ and tanΘ̂. The functions have one form when surface shadowing of the scattered radiation is weak (φi > Θ̂, φs > Θ̂), and another form when surface shadowing is strong (φi > Θ̂, φs ⪅ Θ̂).
On the Effect of Initial Stress on the Propagation of Flexural Waves in Elastic Rectangular Bars
Authors: Clark J. A. , Durelli A. J. , Laura P. A.
Published: October 2005

The dynamics of continuous media subjected to initial stress is of great interest in several fields of applied science and technology: geophysics, oceanography, underwater acoustics, and structural design. Pioneering analytical work in this field was done by M. A. Biot. Few contributions have been made, however, to the experimental treatment of the problem of determining dynamic stress distributions within statically prestressed continuous media. This study deals with an experimental analysis of the propagation of flexural waves in prismatic elastic bars with and without prestressing. The effects of prestressing by axial tension, axial compression, and pure bending are illustrated. Comparisons are made with an approximate theory. The results are extended to bars of other materials by scaling laws.
Tone-on-Tone Masking for Three Binaural Listening Conditions
Authors: Yost William A.
Published: October 2005

The M0-Sm, M0-Sπ and M0-S0 conditions were investigated in a tone-on-tone binaural masking paradigm. Both the signal and the masker were gated sinusoids of the same frequency, duration, and rise-decay time. The data obtained from the two dichotic conditions (M0-Sπ and M0-Sm) indicate that, at low frequencies, detection is based entirely on the interaural phase and intensive differences present in the waveforms. At high frequencies, the interaural phase difference was no longer usable as a cue; thus, detection was the same as in the M0-S0 condition. The interaural intensive difference required for detection was the same at all frequencies. The masking-level differences (MLDs re M0-S0) obtained in the M0-Sm condition were smaller than those obtained in the M0-Sπ condition and were negative in some situations. The data are in agreement with the predictions of the lateralization model proposed by Hafter and Carrier [J. Acoust. Soc. Amer. 47, 1041–1047 (1970)].
Ultrasonic Investigation of Aqueous Solutions of Deoxyribose Nucleic Acid
Authors: O'Brien W. D. , Christman C. L. , Dunn F.
Published: October 2005

The ultrasonic absorption of aqueous solutions of salmon sperm deoxyribose nucleic acid (DNA), molecular weight of the order of 106, was determined as a function of pH in the neutral and acidic regions over the frequency range 5–50 MHz at 25°C. The viscous relaxation frequencies appear to be well below 1 MHz. At neutral pH values, viscosity and molecular conformation appear to contribute little in determining the ultrasonic absorption spectrum. The DNA solution absorption spectrum appears to be similar to that of globular protein aqueous solutions implying that the mechanisms may be the same. The ultrasonic absorption acid titration curves for DNA exhibit maxima around pH 2.6 and 12 [J. Chim. Phys. 66, 81 (1969)] which can be attributed to either or both hydrogen bond transfer and proton transfer as the double helix DNA molecule denatures.
Acoustic Sounding in a Refracting Atmosphere
Authors: Georges T. M. , Clifford S. F.
Published: October 2005

Acoustic refraction by atmospheric wind and temperature inhomogeneities affects the measurements of acoustic sounders in four ways: (a) It displaces the location of the scattering volume relative to its apparent location based on straight-line ray paths. (b) It alters the magnitude of the Doppler shift by changing the magnitude and direction of the wave vector at the scatterer. (c) It changes the scattering angle from that based on a straight-line geometry. (d) It introduces Doppler-shift contributions due to time variations of the atmospheric refractive index all along the sounding path. An idealized model of all these effects on bistatic soundings shows that most refractive corrections are small for present sounding geometries up to heights of about 1 km, but may need to be accounted for as sounding heights increase.
Dynamic Stability of a Cylindrical Shell in an Acoustic Medium
Authors: Deng Zai-Foo , Popelar Carl H.
Published: October 2005

A plane-strain investigation of the dynamic stability of an infinitely long cylindrical shell undergoing breathing oscillations in an infinite inviscid fluid medium is presented. Kinematic nonlinearities of the shell are retained while the fluid is regarded as a linear acoustic medium. A stability criterion which depends strongly upon the acoustic reactance is developed. When the shell is immersed in a fluid, the added mass of the fluid reduces the frequency for parametric resonance. The damping provided by the acoustic resistance proves to be negligible at parametric resonance. The validity of the neglect of kinematic nonlinearities of the fluid is demonstrated by means of an example.
Parametric Acoustic Receiving Array
Authors: Barnard G. R. , Willette J. G. , Truchard J. J. , Shooter J. A.
Published: October 2005

Equations are presented which describe an analytical model of the parametric receiving array and the calculated results are compared to experimental data. Beam patterns and signal levels achieved with an experimental parametric receiving array are presented to extend the ranges and frequencies of previous work conducted in model tanks to parameters of practical significance.
Underwater Acoustic Scattering from Lake Surfaces. II. Covariance Functions and Related Statistics
Authors: Plemons Terry D. , Shooter Jack A. , Middleton David
Published: October 2005

The construction and validation of sample ensembles of reverberation have been considered in Pt. I. These data have been generated by insonifying the rough moving surface of a fresh water lake by narrow-band acoustic signals of comparatively short duration. Included also in Pt. I is a concise account of a basic theoretical model of this scattering process, appropriately modified to the conditions of these experiments. From the above validated data we now determine specifically the various second-order statistics of the reverberation, which are the principal objects of our study. These include the covariance functions and mean intensities. The characteristic nonstationarity of the process appears as an asymmetry of the covariance functions. These experimentally derived statistics are also compared to the corresponding theoretical quantities obtained in Pt. I. Among the critical factors here are the system geometry, including side lobe structure of the beam patterns, and the frequency-selective actions of both the transmitting and receiving apertures on the original, input “electronic” signal. When the assumptions of the model and conditions of the experiment are properly incorporated, good agreement between theory and experiment is obtained.
Multipath Interference Smoothing in Hydrophone Calibrations
Authors: Poché L. B. , Sabin G. A.
Published: October 2005

Development of a computer-controlled calibration system established the need for a simple digital technique for smoothing the fluctuations produced in hydrophone calibration data by interfering signals. The source of the interference is signals arriving at the hydrophone by paths other than the direct one when low-frequency sound is transmitted between a projector and hydrophone closely spaced in shallow water. The simple method of a running mean is remarkably effective, within certain limits, if the span or “window” of the mean is chosen carefully. Fourier analysis of typical data samples confirms the method of choosing the smoothing windows.
Comparable Coupler and Real-Ear Measurements on Supraaural- and Insert-Type Earphones
Authors: Bryant H. W.
Published: October 2005

Tests on supraaural- and insert-type earphones for telephone applications, designed from measurements with real ears and the American National Standards Institute (ANSI) 2- and 6-cm3 calibration couplers, are reported. Disagreements between real-ear and coupler data are rationalized by reducing the basic 2-cm3 volume to 1.3 cm3 and employing an approximate transfer characteristic to relate the supraaural coupler data to a common plane of reference corresponding to the tympanum position. Several experimental couplers for obtaining data within the telephone speech band, which permit measurements on the two types of earphone at the common plane, are described.
Optimized design: characteristic vibration shapes and resonators
Authors: Brach R. M.
Published: October 2005

A technique is developed to find the axial mass distribution of rods and beams based upon desired properties of its first vibrational mode deflection function. This is an inverse Sturm-Liouville problem for rods. The cases of particular interest are when a specified characteristic function does not satisfy the boundary conditions of the problem or continuity conditions. For example, a uniformly strained fixed-free rod vibrating axially cannot exist because the strain must be zero at the free end. Using calculus of variations, a method is developed whereby the rod or beam is found whose first characteristic function can be as close as possible to the specified unattainable function. This is done for linearly elastic axially nonuniform materials vibrating axially or transversely. Examples include the application of the technique to the design of ultrasonic resonators.
Axial-flexural vibration of frameworks using finite-element approach
Authors: Yang T. Y. , Sun C. T.
Published: October 2005

A finite-element procedure for predicting the frequency of axial-flexural coupling vibration of frameworks is presented. In addition to the rectilinear beams, the formulation and the procedure are also shown to be highly accurate in the analysis of axial-flexural coupling vibration of a portal frame by comparing the results with an analytical solution presented herein. Additional examples include a two-bay portal frame and the single-bay multi-story frames. It is found that in the case where the horizontal beam contains floor masses or the frame is composed of multiple stories, substantial discrepancies exist between the axial-flexural frequencies and the flexural frequencies. In those cases, the axial motion is no longer negligible in the vibrational analysis.
Time-varying multipath interference of broad-band signals over a 7-NM range in the Florida Straits
Authors: DeFerrari Harry A.
Published: October 2005

The frequency response function of a propagation channel is formulated by the coherent (vectorial) summation of CW signals arriving via many ray paths between source and receiver. Six months of continuous measurements of water temperature from a moored thermistor string in the Florida Straits are analyzed to determine the temporal variation of the sound speed profile. The observed average profile and its temporal variations are shown to be closely modeled by fitting the data with two layers of linear sound speed gradient. In order to investigate the effects on propagation of temporal variations of the two layers, a model of Refracted Bottom-Reflected (RBR) propagation is developed for the particular case of a bottomed source and receiver. Model computations determine the relative influence of the parameters of the two layers upon the interference of broad-band signals. The general features of multipath interference which are observed in the Florida Straits are presented and discussed. Model simulations of multipath interference are used to interpret experimental results. Some characteristics of the propagation channel (e.g., bandwidth of an interference fade) are shown to depend on average values of the model parameters, while others (e.g., CW amplitude) depend on small fluctuations about the averages and thus cannot be estimated with idealized propagation models. For typical profiles the gradient near the bottom determines the average properties of the channel frequency response function.
Scattering of plane wave by infinite semicylindrical bosses with random radii on a plane surface
Authors: Klos W. A. , Hayre H. S.
Published: October 2005

This paper covers both theoretical and experimental phases of the subject of scattering of a plane wave incident on infinite semicylindrical bosses of random radii with periodic spacing. The probability density function of the radius of a semicylinder is assumed to be uniform, and the spacing between the centers of adjacent bosses is maintained constant. The spacing is so selected as to make the shadow effects negligible for the angles of incidence considered in this paper. The scalar form of the Helmholtz integral formulation was employed, although some of the inherent assumptions are invalid, owing to discontinuities in the surface. A comparison of the lobe structure (scintillation) of the experimental and theoretical angular acoustic-intensity scatter patterns, in particular, the main specular lobe, shows a reasonable agreement with the additional inference about the weakness of the assumption of the model material being rigid.
Propagation of acceleration waves in a binary nonreacting mixture
Authors: Leininger J. R. , Nachlinger R. Ray
Published: October 2005

In this work, the behavior of acceleration waves in a two-constituent mixture is examined. This examination is based on a purely mechanical theory that does not consider reactions. Each of the constituents is assumed to behave in a quasielastic manner, and no restriction is placed on the amplitude of the waves.
Focusing of stress waves in an elastic sphere
Authors: Wheeler Lewis
Published: October 2005

This paper concerns the effect of focusing upon the strains in an elastic sphere excited by spherically symmetric surface loading. The analysis is carried out on the basis of the solution to the corresponding boundary-initial value problem. This solution, which is found with the aid of the Laplace transform, is given in a form well suited to assessing the consequences of roughness in the loading.
Sounding mechanism of singing sand
Authors: Takahara Hikaru
Published: October 2005

The musical sound from the singing sand was observed with a synchroscope, and the frequency analysis was performed. With repeated application of forces the musical sound from the singing sand decreases and finally disappears. Recovery of the musical sound from such wasted singing sand was tried. For the purpose of investigating the character of the particles of the singing sand, the noise wave emitted from it under a large load was studied. It is concluded that the characteristics of noise wave from the singing sand depends on the friction properties of the sand particles of comparatively uniform sizes and of smooth surfaces. This fact seems to be closely related to the mechanism of musical sound emission from the singing sand.