bluuebunny/crossref_metadata_2025 huggingface dataset:
Bubble Growth Rates and Thresholds of Rectified Diffusion
Authors: Eller Anthony
Published: November 2005

A gas bubble that ordinarily would dissolve may be seen to grow by rectified diffusion if it is driven by an acoustic field whose pressure amplitude exceeds a threshold value. This threshold pressure has been measured as a function of bubble radius for air bubbles in water that is saturated with dissolved gas. The acoustic frequency was 26.6 kHz. The rate of bubble growth or dissolution, when the acoustic pressure was not equal to the threshold value, was also measured. The experimental results are compared with predictions of theory.
The Damping of Perturbations on a Plane Shock Wave
Authors: Briscoe M. G. , Kovitz A. A.
Published: November 2005

A plane shock front, propagating normal to itself through a uniform ideal gas, is given a sinusoidal perturbation at an initial instant of time. The subsequent motion of the front and the gas in its wake is analyzed using a linearized system of equations and auxiliary conditions. The analysis follows closely that due to Zaidel [J. Appl. Math. Mech. 24, 316–327] for a shock wave produced by a corrugated piston. Two cases are considered: (a) the normal shock reflection from a sinusoidal wall such that the usual wall boundary conditions are satisfied; (b) the free-space damping of a sinusoidal perturbation such that there be no disturbance on the backward propagating weak discontinuity emanating from the initial position and time of the perturbed shock. For sufficiently small shock Mach numbers the presence of the wall does not have a strong effect on the damping rate; damping is caused primarily by the direct interaction of the disturbed wake with the perturbed shock front. Experimental and theoretical results corresponding to Case a compare very favorably with each other. Case b has not been subjected to experimental study. The analysis may be extended to arbitrary initial shock shapes by Fourier integral or Fourier series techniques.
On the Existence of Focusing Zones along the SOFAR Axis
Authors: Hirsch Peter
Published: November 2005

The typical SOFAR pulse is composed of many separate arrivals that have propagated along different, multiply refracted paths. The energy that propagates straight along the channel axis is called the axial arrival. Goodman and Duykers [J. Acoust. Soc. Am. 34, 960–962 (1962)] show that, if the sound-speed profile about the axis is approximately parabolic, then the axial arrival should be periodically focused at ranges that are integer multiples of a characteristic distance that is about 6 NM in the North Atlantic. However, it is known that the behavior of the paraxial arrivals is very sensitive to the precise form of the profile [see e.g. Hirsch and Carter, J. Acoust. Soc. Am. 37, 90–94 (1965); Williams and Horne, J. Acoust. Soc. Am. 41, 189–198 (1967)], so that the question of the existence of focusing zones in the ocean sound channel has remained open. To answer the question, one can use a result first pointed out by Slichter [Physics 3, 273–295 (1932)], that focusing in space implies focusing in time. Thus, the nonexistence of axial focusing zones in typical SOFAR propagation can be inferred from the time dispersion of the arrivals. [Work supported by the Bureau of Ships, U. S. Navy.]
Representation of SOFAR Speed by Spherical Harmonics
Authors: Johnson Rockne H.
Published: November 2005

Accurate position fixing by SOFAR requires that sound travel times along the paths involved be accurately known. A general method for providing travel times along any path in a given region is by representing the SOFAR speed as a continuous function of latitude and longitude. Such a function has been constructed for the Pacific Ocean. The basic data were hydrographic measurements, from which local SOFAR speed data were obtained, together with explosion travel times, from which average velocities along particular paths were calculated. No allowance was made for seasonal variation, which might be predictable in high latitudes. The explosion data, which might be viewed as calibrations, have been obtained only in the northeast Pacific. Both types of data were combined in a single matrix equation to yield estimates of the coefficients of a set of spherical harmonic functions. Classical harmonic analysis was precluded by the mixed data as well as by its irregular spacing. Fougere's method of harmonic analysis, which orthogonalizes the condition matrix by the Gram-Schmidt process, was applied. Termination of the series at degree six left a standard deviation of the hydrographic data of 2.0 msec.
Normal Mode Solution in a Medium with Curvilinear Velocity Profile
Authors: Hamzeh S. M.
Published: November 2005

The solution of the wave equation is obtained for a fluid medium with a curvilinear velocity profile. The reciprocal of the velocity squared is represented by an nth-degree polynomial as a function of depth. This leads to depth-dependent special functions numerically evaluated from recurrence relations by digital subroutines. The general solution is expressed as an integral in the wave-number space. The integrand is analytic in the cut complex wavenumber plane except at a countably infinite number of poles that characterize the normal modes of propagation. The residue theorem transforms the integral expression to an infinite series, the normal modes contribution, plus a branch line integral that vanishes in the long-range limit. In the short-range limit, the branch line integral leads to a wave diminishing in amplitude as the inverse square of the range and having a phase velocity equal to the speed of sound in the ocean's bottom.
Ultrasonic Simulation of Shallow-Water Sound Propagation
Authors: Rhodes Richard A. , Goodnight Lyman E.
Published: November 2005

A. B. Wood's ultrasonic modeling technique is being used to investigate sound propagation in the shallow ocean in connection with a project on basic aspects of underwater speech and hearing conducted by the University of Florida's Communication Sciences Laboratory. One actual problem simulated is one where measurements were taken in the Gulf of Mexico at the U. S. Navy Mine Defense Laboratory's Stage I, in 31 m of 76°F water over a flat, sandy bottom. The ultrasonic simulation experiment used a water-filled concrete tank 3 ft×4 ft×4 in., side-lined with sound-absorbing rubber matting, and bottom lined with soft rubber to simulate sand. The transducers were two matched pairs of PZT crystals of frequencies 658 kHz and 1009 kHz with wire probes projecting beneath the water surface. Appropriate distance scaling was used to simulate seven frequencies from 0.125 to 8 kHz. Fair agreement was found with the large-scale experiment. Refinements in the simulation technique are being sought. Also calculation by normal mode theory is being undertaken. [Work supported by the U. S. Office of Naval Research.]
Changes in the Cochlear Microphonic Resulting from Exposure to a 5.0-kHz Tone
Authors: Price G. Richard
Published: November 2005

As our initial effort in the investigation of the effect of high-intensity sound on hearing, round window potentials were recorded from 34 cats as they were exposed to a 5.0-kHz tone. Exposure times totaled 80 min, and intensities ranged from that intensity necessary to produce a maximum in the cochlear microphonic to 30 dB above that intensity (actual sound-pressure levels ranged from 99 to 138 dB). Measures of the shift in sensitivity following stimulation were made for 12 frequencies at 10 times during the experiment. Data indicate that loss occurs at a rate that is linear in time at high intensities and linear in log time at the lower intensities. The pattern of damage was wide spread with most of the losses occurring below 5.0 kHz.
AC Potentials Inside the Organ of Corti
Authors: Lawrence Merle
Published: November 2005

Previous studies have shown the tectorial membrane to be at a nearly zero potential [Ann. Otol. Rhinol. Laryngol. (July 1967)] surrounded by the negative potential of the cortilymph and the positive potential of the endolymph. The first step in determining the role of this polarization in the energy transformation process within the cochlea is a determination of the magnitude of the ac potential in the dc potential regions at various points along the basilar membrane in response to frequencies from 150 Hz to 10 kHz. These recordings are made through electrolyte filled glass microelectrodes with separation of the ac and dc components recorded through the same electrode. Phase shifts as a function of electrode tip position as the various dc potential areas above the basilar membrane are penetrated are also recorded. Results are interpreted as of significance in the process by which vibrations are transformed into the cochlear ac potential. [Research supported by PHS grants.]
Development of Hypersensitivity to Acetylcholine by the Denervated Cochlea
Authors: Daigneault E. A. , Brown R. Don
Published: November 2005

Previously described experiments [Arch. Int. Pharmacodyn. 162, 20 (1966)] have shown that acetylcholine bromide (20 μg/dose) injected into the arterial supply (i.a.) of the cochlea will produce suppression of the N1 recorded from the round window of the cat. This depression is similar to that produced by stimulation of the olivocochlear bundle (Nature 192, 1263 (1961)]. With such evidence and other indications from the literature, it is possible to consider that some role may be played by acetylcholine in the cochlea. In an acutely sectioned cat in i. a., injection of acetylcholine is as effective as before the section (25% N1 depression, 17 observations). We concluded that the system responsive to acetylcholine is in the cochlea proper. Subsequently, cats that had previously had their left eighth cranial nerves sectioned from two to five days were tested as to their responsiveness to i.a. acetylcholine. In six animals, four or five days after section, 2 μg of acetylcholine produced a 22% depression of N1. This measured hypersensitivity is presented as further evidence that acetylcholine is active in either initiating a mediator release in the organ or is a mediator itself.
Radiated Flow Noise
Authors: Skudrzyk Eugen J. , Haddle G. P.
Published: November 2005

Recently, Lighthill used an improved estimate for the time scale of flow noise, which leads to more than 500 times greater radiation-field pressures for boundary-layer noise. The new theoretical predictions approach the levels generated by rotating cylinders or by large ships. The new theory shows that radiation field is generated in the strongly intermittent outermost part of the boundary layer. The radiation field generated by small vehicles is much greater than that of large ships, because of their smaller stability and the greater intermittency of the turbulence. Radiated flow noise is generated by the boundary-layer turbulence directly. Flow-excited wall vibrations contribute to radiated noise only at frequencies below 500–1000 cycles, provided the boundary layer is thick and the vessel walls thin.

Measurements showed there was practically no difference between the radiation field generated by a relatively thin aluminum-shell buoyant unit, or by one made of solid wood. Radiation-field measurements obtained by three independent methods will be presented: (a) by a hydrophone in the non-turbulent region of the buoyant unit, (b) by a nearfield insensitive hydrophone in the boundary layer, and (c) by three hydrophones at a distance 60 ft from the rising buoyant unit at depths of 250, 150, and 80 ft. [Sponsored by Naval Ordnance Systems Command.]
Turbulent Boundary-Layer Induced Pressures Transduced through a Fluid Loaded Plate
Authors: White Pritchard H.
Published: November 2005

The turbulent boundary-layer pressure field induces flexural vibrations in an adjacent plate, which in turn radiates an acoustic pressure field. The flexural waves in the plate are strongly influenced by the presence of surrounding fluid acting as an additional effective mass or damping. The pressure in the immediate vicinity of the plate is due to the incompressible hydrodynamic nearfield of the subsonic resonantly driven flexural waves. This pressure field decays exponentially away from the plate to reach a limiting value determined by the acoustic components of the turbulence itself. The spatial characteristics of the pressure field also change from the near to farfield, reflecting a downward shift in the wavenumber spectrum. [This work supported by U. S. Navy Ship Research and Development Center.]
Peak Velocity Spectrum of a Flat Plate Excited by Turbulent Flow
Authors: Strawderman Wayne A. , Brand Ronald S.
Published: November 2005

A mathematical expression predicting the maximum possible plate velocity spectrum as a function of plate and flow parameters is derived based on results of a theoretical investigation of the response of a simply supported flat plate to excitation by a turbulent boundary later. The maximum possible plate velocity spectrum is termed the peak velocity spectrum. Computed peak velocity spectra compare favorably with existing experimental information. The resultant expression provides an economical method of predicting the maximum expected plate velocity spectral density for a flat plate excited by a turbulent flow at frequencies above the first few natural modes, Although certain details of the true plate velocity spectrum are not preserved in the plate peak velocity spectrum, effects of major parameters are preserved. Thus, the peak velocity spectrum supplements the knowledge of flow induced phenomena and provides practical engineering results.
Observation of Turbulence in the Acoustic Boundary Layer
Authors: Cosgrove Michael A.
Published: November 2005

Turbulence in acoustic flow causes random fluctuations in the particle displacement amplitude. A tracer-particle method has been used to detect boundary-layer turbulence. Micron-size oil drops are injected into an air-filled waveguide, dark-field illuminated, and photo-micrographed. With an exposure time slightly longer than one period of oscillation, the image of an oil drop appears on the film as a streak whose length is proportional to the displacement amplitude. Optical reflection from the mirror-smooth boundary produces a companion streak. The streaks are separated by a distance proportional to the height of the oil drop above the boundary. For a 900-Hz progressive wave at a SPL of 140 dB, displacement amplitude measurements agree with laminar-flow theory. At 145 dB, however, measurements are widely scattered about the laminar-flow curve for heights between 70 and 140 μ. It is concluded that the threshold of turbulence at this frequency lies between 140 and 145 dB. [Work supported by the Mechanics Division, AFOSR, Office of Aerospace Research.]
Ultrasonic Attenuation Measurements at Pressures to 10 000 kg/cm2
Authors: Hagelberg M. Paul , Johnson Walter H. , Holton Gerald
Published: November 2005

Improvements in previously reported techniques [cf. Bull. Am. Phys. Soc. 77, 78 (1966); Acoust. Soc. Am. 39, 1224 (1966)] are described by which reliable ultrasonic attenuation measurements in liquids may be made at pressures to 10 000 kg/cm2. Some of the problems involved both in making the measurements and in analyzing the data obtained are described. Results are presented for some typical liquids and the observed absorption compared to the absorption due to shear viscosity. [This work is supported by the U. S. Office of Naval Research.]
Effect of Temperature on the Rotational and Vibrational Relaxation Times of Some Hydrocarbons
Authors: Hill Garnett L. , Winter Thomas G.
Published: November 2005

It has been demonstrated previously that increasing temperature has the effect of increasing the relaxation frequency of a vibrational relaxation and decreasing the relaxation frequency of a rotational relaxation. This effect can be seen clearly in both the ultrasonic absorption and velocity data presented. Measurements covered one to 100 MHz/atm and room temperature to 800°C. In room temperature methane, only the lower part of the rotational relaxation can be seen at 100 MHz/atm, but by 500°C the inflection point of the vibrational dispersion curve has moved up to 1.5 MHz/atm while that of the rotation has moved down to 50 MHz/atm. Two absorption peaks are clearly discernible. By 800°C, the dispersion is continuous over the entire frequency range. Similar measurements on ethylene show roughly the same behavior. In ethane, there are two vibrational relaxations and the effect of temperature on the acoustic behavior is quite different. [Work supported by the U. S. Army Research Office, Durham.]
Vibrational Relaxation in Nitrogen with Water Vapor and Carbon Dioxide Contaminants
Authors: Henderson Malcolm C. , Coakley Raymond ,   OSFS, Bry Jacques
Published: November 2005

The pressurized Kundt's tube developed in this laboratory has been used to measure the napier (relaxation) frequency of nitrogen in both binary and ternary mixtures with water vapor and carbon dioxide. Carried out at about 175°C, where the relaxing vibrational specific heat of nitrogen becomes large enough to be readily measureable, both contaminants shift the Napier frequency upward by amounts simply proportional to their molar concentrations: water vapor by 300 Hz per mole%, carbon dioxide by 250 Hz per mole%. However, preliminary work indicates that when both are present the shift is not the simple sum of the individual effects, but that there is considerable synergism. Such a synergistic effect is indeed to be expected on theoretical grounds. [This work was supported by the Office of Naval Research.]
Measurement of Viscoelastic Properties of Polymers by Ultrasonic Methods
Authors: Smithson J. R.
Published: November 2005

Yasaku Wada [J. Phys. Soc. Japan 15, 2324 (1960)] has proposed a method of calculating the real and imaginary parts of the bulk modulus of a polymer from measurements of the sound velocity and absorption coefficient of a water suspension of the polymer. An analysis of the propagation of measurement errors through the bulk modulus calculation, shows that errors in sound velocity are magnified in the calculation, but existing methods of velocity measurement are sufficiently accurate to allow worthwhile results. A feasibility study of the method has been made using some special suspensions of polybutadiene which were prepared by Goodrich Rubber. These suspensions were unique in that they contained very narrow bandwidths of particle sizes. Studies have considered particle size, concentration, temperature, sound frequency, and effect of dissolved salts and soaps in the suspensions. Results indicate that the method has a considerable range of usefulness. [Supported by the Office of Naval Research.]
Vocal-Tract Perturbation Functions
Authors: Heinz John M.
Published: November 2005

In recent years, Webster's horn equation has been widely used as the basis for an approximate description of the acoustic behavior of the human vocal tract. Starting from an assumption of the validity of this equation, a procedure for determining for an arbitrary vocal-tract configuration those first-order changes in the configuration that will effect changes in one and only one formant frequency (or, alternatively, one and only one lip impedance pole or zero) is presented. Examples illustrating the iterative use of this procedure for determining vocal-tract configurations that correspond to specified impedance pole-zero patterns are given together with a discussion of some of the practical difficulties that arise in this application. [This work was supported in part by Special Fellowship from the National Institute of Neurological Diseases and Blindness, Public Health Service while the author was a guest at the Department of Speech Communication, The Royal Institute of Technology, Stockholm, Sweden.]
Acoustic Implications of Interspecies Communication
Authors: Lilly John C. , Truby Henry M. , Miller Alice M. , Grissman Frank
Published: November 2005

When, in interspecies exchange of information, the dominant modes of the communication are vocal and acoustic, some of the physical limitations imposed upon the communication are shown by the hearing curves and the acoustic energy output curves. Additional limitations are shown in the difference frequency limen curves and in certain time-pattern perception limitations. One such communication system is the interlock or feedback between a single individual Homo sapiens (Hs) and a single individual Tursiops truncatus (Tt). The speech output of Hs was measured with a high-frequency microphone; detectable amounts of energy were found above the generally accepted speech band, up to the order of 60 kc. This high-frequency energy is detectable by Tt as is shown by its hearing curve from 400 Hz to 160 kHz. The usually accepted limits for Hs-Hs transmissions for 100% intelligibility are from approximately 100 Hz–10 kHz. The Hs-Hs feedback control thus is limited to approximately 10 kHz; i.e., energy above this limit is not controlled nor used by Hs. In the Hs-Tt transmission, this energy functions as an adequate stimulus to Tt. Thus, to Hs this high-frequency energy is unknown noise but can be mistaken by Tt for signals. Further consideration of the physical limitations on Hs-Tt vocal exchanges are considered with a feedback diagram and quantitative calculations based on the hearing curves and the sonic-ultrasonic output of Hs and Tt. Thus, in treating another species with a different hearing curve and a different sonic energy output, it is imperative to have quantitative physical measures in order to find channels that are adequately open both ways between the different species. Such considerations determine necessary acoustical and electrical transforms of the outputs and inputs from and to each member of the different species. [Work supported in part by AFOSR and NIH, NINDB.]
Cryprint Categories in Newborn-Infant Cry-Sound Analysis
Authors: Truby H. M.
Published: November 2005

The first 10 yr of an ongoing, long-range, acoustic and acoustigraphic (sound-spectrographic, jet-written oscillographic, and other visible-acoustic) analysis program have been centered upon the investigation of paranatal, immediately postnatal, and neopostnatal cry-sound in human infants. This program has recently been extended to include the examination of postnatal periods beyond the drastically transitional neonatal period. Of the thousands of sound spectrograms of newborn-infant cry-sound examined, at no time has any sequence “repeated,” either in the same infant or in different infants, yet, based upon 20 yr of intimate experience with sound-spectrographic analysis of adult speech and other acoustic phenomena, it seems evident to the author of this paper that each infant unambiguously demonstrates his individuality in his cry-sound patterning… i.e., his cryprint. The prospect of ultimately validating cryprinting as a reliable analog to footprinting and fingerprinting was proposed at 60th ASA Meeting in San Francisco, 1960 as was the prospect of establishing the visual-acoustic patterning of neonatal, or even paranatal, cry-sound as supplementary clinical-diagnosis criteria in the early detection of brain damage and other serious neurological impairment. The research-in-progress status of these studies will be discussed and demonstrated in acoustigraphic and acoustic form. [Work supported by NIH: NICHD, and by United Cerebral Palsy Research and Educational Foundation.]
Optimum Transmit and Receive Beam Patterns for Sonata Operating Against Reverberation
Authors: Liggett W. S. , Pitassi D. A.
Published: November 2005

Since the shape of the transmit beam pattern affects not only the strength of the echo but also the spacial correlation of the reverberation, optimum design of this pattern may improve performance. Following transmission of a narrow-band pulse, our system decides if an echo from a slowly moving target is present in the volume reverberation and noise. The target direction and range are known a priori. Our transmit pattern may be adjusted by applying amplitude weightings and phase shifts to the transducer inputs. Using a well-known reverberation model, we obtain the beam former for the Bayes optimum receiver. Once the optimum receiver for arbitrary transmit pattern has been found, further reduction in the error probabilities is obtained by the proper choice of transmit shading coefficients. As examples, we investigate line arrays with half-wavelength spacing. When the reverberation power is much greater than the noise power, the optimum transmit and receive patterns do not have their maxima in the target direction. When noise that is independent between hydrophones dominates, unshaded patterns are optimum.
On Measuring the Stationarity of Ambient Sea Noise
Authors: Parkins B. E. , Bogert B. P.
Published: November 2005

Efforts to determine the low-frequency spectrum of ambient sea noise have shown that there exist slow variations in the noise power in the ocean. These variations amount to a modulation of a “short-term” estimate of the frequency spectrum of the noise. A search for this modulation has been made by filtering the sea noise from a single deep hydrophone into nonoverlapping frequency bands and then detecting and recording the envelopes of the variations within these bands. The envelope variation has been investigated by examining the self- and cross-spectra of the set of envelopes for the bands analyzed. From these results, the coherencies of the covariation between bands of frequency versus the modulation periods were calculated. For a stationary random process, the coherency should vanish. The data analysis, thus far, which includes stretches up to one day in length, shows very small coherence between bands centered an octave apart. This implies that either the noise is almost stationary or the “modulation” is incoherent for these frequency separations. [Work supported by the U. S. Navy Office of Naval Research.]
Algorithmic Selection of Acoustic Waveforms
Authors: Lord Norman W.
Published: November 2005

The choice of acoustic waveform is studied within the category of widely spaced FM pulses for the goal of optimum resolution between overlapping arrivals. For a given average frequency and pulse time length, it is analytically apparent that there exists a wide variety of monotonic F-t shapes that have the same average frequency, time length or number of cycles, and frequency difference between initial and final cycles. It is then shown how to program the calculation of autocovariance among all such waveforms using a preliminary calculation of a subset of the partitions of an integer sum representing the pulse time length. The number of integers in the partition is restricted to be the number of cycles with the smallest integer representing the highest frequency and the largest representing the lowest. The most prevalent choice, for an optimum decline among the autocovariance side-lobe peaks, has a frequency variation that is small at the ends of the pulse and high near the center. It is also possible to seek along the courses of spreading the frequency extremes and changing the pulse length for F-t shapes that further minimize the side lobes. [Hudson Labs. of Columbia Univ. Informal Documentation No. 137. This work was supported by the U. S. Office of Naval Research.]
Acoustic Spectrum Analysis with Coherent Optics
Authors: Stanford George E.
Published: November 2005

An optical spectrum analyzer has been assembled at USL to investigate the application of one- and two-dimensional transforms in SONAR signal processing. In the one-dimensional mode, the analyzer was used to examine a sample of low-frequency marine noise. Of special interest was the ability to view the dynamic spectrum of the noise field. Some parts of the spectrum fluctuated rapidly, whereas other portions varied very slowly. The stronger lines were more nearly stationary, varying slowly in intensity and spectral position. Some of the lines split into numerous less intense lines, eventually regrouping to form a single well-defined spectral line. The analyzer was used also in the two-dimensional mode, performing as a combined direction finder-spectrum analyzer. A synthetic signal, simulating the output from a continuous linear array, increased the intensity of the two-dimensional spectrum by a factor of 8.7 compared with that of the one-dimensional, single-channel spectrum. The two-dimensional transform also produced information regarding signal directionality, appearing as a rotation of the spectrum in the output plane.
Real-Time Display of Sound Holograms by KD*P Modulation of a Coherent Light Source
Authors: Boutin H. , Mueller R. K.
Published: November 2005

It is possible to reconstruct optically a sound hologram by reflecting a laser beam from the pattern formed on the water surface [R. K. Mueller and N. K. Sheridon, Appl. Phys. Letters 3, 328 (1966)]. The acoustically illuminated object is then viewed in real time but the quality of the reconstruction is poor because of aberrations due to streaming and oscillatory surface disturbances. A way of improving the real time reconstruction process is presented, in which the holographic pattern is recorded on the surface of a piezoelectric crystal (quartz), immersed in the water, and then forms the end wall of a Sokolof-type electron tube. A scanning electron beam reads off the corresponding voltage pattern obtained on the surface of the piezoelectric crystal. It produces an output signal that is then applied to a deuterated KDP crystal (KD*P) scanned by an electron beam synchronized with that of the first tube. It is therefore possible to modulate the index of refraction of KD*P (Pockels effect) and obtain phase modulation corresponding point by point to the holographic pattern recorded on the quartz surface. Illumination (reflection or transmission) of the crystal with laser light will permit optical reconstruction of acoustically illuminated objects. This device permits a scale change of the hologram that reduces aberrations.
Face Plates for Image Converters
Authors: Karplus Henry B.
Published: November 2005

Electronic image converters have been built largely as demountable systems with attached vacuum pumps for experimental purposes. Permanently sealed systems with large face plates requiring a high vacuum on the inside and good acoustic coupling to the transducer through the wall have had only limited success. The approach used here has been a separation of the vessel wall and transducer material. Three bonding systems were investigated: (1) cement, silicone rubber showed good stability; (2) low melting point alloys, and (3) direct heat bond of barium titanate to an Inconel surface.
Nearly Spherical Lenses
Authors: Feldman H. R. , Lord G. E.
Published: November 2005

A unidirectional geometrically perfectly focusing lens can be made by shaping appropriately the interface between homogeneous lens media. For good geometric focusing over a wide angle, the lens should be as spherical as possible. A single component lens that focuses a perfect image of an object at infinity is a conic section of eccentricity 1/n, where n is the index of refraction of the lens material. The limitation on n due to the lack of transmissive materials with very low acoustic velocity requires that such a lens be quite aspherical. This difficulty is not inherent in multicomponent lenses. Perfectly focusing shapes have been determined for two-component lenses with spherical outer surface. The meridional and sagittal focusing properties of these lenses have been studied for obliquely situated objects. With a proper choice of lens parameters, the internal interface is not required to deviate from sphericity by more than about 2%, so that the attainment of a perfect geometric focus in the forward direction does not seriously degrade the imaging of objects situated at very wide angles.
Acoustic Field in a Luneberg Lens
Authors: Lord G. E. , Feldman H. R.
Published: November 2005

A Luneberg lens, which is a perfectly focusing omnidirectional spherical lens, has been subjected to a wave analysis. Plane radiation incident on a fluid lens was assumed. The separability of the scalar Helmholtz equation for the lens region permits the representation of the internal acoustic field as an expansion in Legendre polynomials and radial functions. The radial equation obtained from the separation was solved in integral form from which the necessary recurrence relations were obtained. Beam patterns at and relatively near the focal point were obtained for moderate wave number-aperture products (k0∼a80). Calculations for high frequencies are hampered by the lack of sufficiently general schemes for function generation. The beam patterns so obtained are quite similar to those obtained for comparable spherical fluid lenses of uniform refractive index. Lens gains and beamwidths do not differ significantly in the two cases. In general, the side lobes for the Luneberg lens are relatively high and decrease relatively slowly in magnitude as the polar angle increases.
Basic Problems in Underwater Acoustic Imaging
Authors: Davidson J. Blaine , Hull Joseph
Published: November 2005

The basic elements of an underwater acoustic imaging system are presented. Each element that introduces serious problems in the design and construction of a practical system is discussed and known ways of solving the problems are outlined. Problems of specular reflection, range-definition tradeoffs, size, weight, cost, lenses, deep submergence pressure, and data rate are presented. Techniques utilized in the HYDROCON system are used as illustrations of one practical embodiment of the principles of a system. Finally, new ideas are presented to suggest areas in which techniques now under development may provide solutions to some of our current problems.
Acoustical Design and Testing of the Centenary Auditorium of Madras University, Madras
Authors: Ramakrishna B. S.
Published: November 2005

The paper describes the acoustical design and testing of a 3250-seat multipurpose auditorium. Among the problems discussed here is the question of what reverberation time is optimal for a hall that uses a sound reinforcement system to augment the direct sound. The design and performance of a sound reinforcement system for the hall is also described. The hall has a volume of about 800 000-ft3 and a midfrequency RT of 2.3 sec when empty and 1.7 sec when full. The bass ratio is approximately 1.3. The maximum variation of the sound level over the seating area is 4.5 dB. The noise level (on C-weighting) in the fully occupied hall is 42±1 dB without air conditioning and 52±1 dB with air conditioning.
Acceptability of Footfall Sounds in Apartments
Authors: Watters B. G.
Published: November 2005

We have studied the acceptability of intruding footfall sounds in apartments. In controlled laboratory experiments, the signal frequency range, signal duration, and ambient noise levels have been varied to correspond to variations in floor surface compliances, room RT's, and other factors typical of real apartments. The test subjects, experienced apartment dwellers, compared the acceptability of footfalls with intruding speech at that just-intelligible level previously found marginally acceptable in buildings. The footfalls they judged as acceptable as the reference speech signal were just detectable, i.e., very close to the masked threshold. The condition of constant acceptability, as footfall level, center frequency, bandwidth, and reverberation are varied, requires the quantity (WT)12S0/N0 to be held constant, where W is the effective signal bandwidth, T is the effective signal duration, S0 and N0 are the signal and noise intensities per hertz. A proposed floor rating scheme is shown to be similar to one developed for the Insulation Board Institute. However, neither of these compares with the ISO R140 procedure that deals, not with footfalls, but with a more intense impact. This work was supported by the Armstrong Cork Company.
Impedance Tube Used as a Source of Known Acoustic Power
Authors: Jack William A.
Published: November 2005

In an open-ended tube with negligible losses, the standing wave pattern is probed for maximum and minimum SPL's at the time the tube is generating a pure-tone steady-state level in the room under test. The power emitted is a function of these levels and the tube-section area. The room average SPL is a function of this power and the effective sabins in the room. These sabins can be evaluated. If more absorbing material is introduced, the effective sabins added can be evaluated. With simple sources, such as a fixed rpm fan or a fixed voice coil current loudspeaker, possibly valid objections have been made that adding more absorbing material could change the source output in an unknown manner. With the tube method, it is of no consequence whether or not the changed acoustical environment reacts to change the power, as the output is measured for each condition. It would be desirable to extend the method to handle warble tones and narrow bands of random noise.
Sound Decay Rates in Various Conference Rooms as Measured by the Automatic Decay-Rate Meter
Authors: Harvey F. K. , Presti A. J.
Published: November 2005

The automatic decay-rate meter described by A. J. Presti [J. Acoust. Soc. Am. 40, 1267 (A) (1966)], has been used to examine the sound decay in a number of conference rooms, with special emphasis on those having fast decay rates. Results are compared with determinations from several different types of oscilloscope presentations. Advantages and limitations in the use of the decay-rate meter will be discussed.
Acoustic Scattering of FM Pulses from Aluminum Spheres in Water
Authors: Mikeska E. E. , Hickling R.
Published: November 2005

Experimental measurements of acoustic backscattering of FM pulses from a family of precision-solid and hollow-aluminum spheres of 7 in. o.d. are presented and compared with computed echo pulse forms. The present paper is an extension of work reported by Diercks, Goldsberry, and Hickling for 5-in.-diam spheres [J. Acoust. Soc. Am. 40, 1258 (A) (1966)]. The spheres studied had i.d./o.d. ratios of 0.95, 0.8, and 0.0, with either air or water inside the hollow spheres. The incident FM pulses had a nondimensionalized center frequency of ka = 20 (approximately 54 kHz) with nondimensionalized frequency ranges of 15–25 and 10–30 during the pulse. Incident pulse lengths were selected in the nondimensionalized form Δτ = 0.5, 1.0, or 5.0, where Δτ relates the range extent of the pulse to the radius of the sphere according to 2Δτ = c2Δt/a, where 2Δt is the pulse length in seconds, c is the velocity of sound in water, and a is the radius of the sphere. Detailed comparison of experimental and theoretical results shows generally good agreement in frequency structure and amplitude for FM pulses having a range extent equal to or shorter than the sphere diameter. Comparisons for longer pulses are also shown. [This work was done under contract with the U. S. Office of Naval Research, Code 463, and the U. S. Naval Ordnance Test Station, Pasadena, California.]
Acoustic Scattering by a Soft Cylinder
Authors: Goldsberry T. G. , Grace O. D.
Published: November 2005

Backscattering coefficients have been computed for an infinite, soft cylinder over the range of acoustic radii, ka, from 0.5 to 25. Scattering patterns in a plane perpendicular to the cylinder axis have been obtained for selected ka values. Experimental measurements of acoustic scattering in water were obtained using a cylinder 10 cm in diameter machined from low-density Styrofoam. The experimental measurements cover the ka range 1.2 to 21. Excellent agreement between theory and experiment were obtained over this ka range and indicate both the validity of the computations and the usefulness of low-density Styrofoam as an acoustically soft material in underwater acoustics. [This work was done under contract with the Office of Naval Research, Code 463.]
Diffraction by a Wedge
Authors: Ingram John D.
Published: November 2005

The diffraction of waves by a wedge-shaped boundary separating two media has long been an open question in acoustics. In this paper, an exact solution is presented for such a physical system with arbitrary wedge angle and source placement. Kontorovich-Lebedev transforms are used to solve the equations of motion and to analyze the boundary conditions. This analysis results in a singular integral equation for the transformed potential. Function theoretic methods are used to reduce this equation to a Fredholm equation with a symmetric kernel. The exact solution is then given in terms of the eigenfunctions of the symmetric kernel. The principal contributions of this work are the production of a joint distribution for the radial eigenfunctions (with two distinct wave speeds) in cylindrical coordinates and the method used to reduce a nondegenerate singular integral to a Hilbert-Schmidt equation. These two techniques, however, not only allow the solution of the scalar problem reported here, but also show the way to solution of the vector problems for electromagnetic and elastic fields.
Experimental Investigation of Surface Wave Phenomena by Sound Pulse Techniques
Authors: Harbold Mary L. , Steinberg Bruce N.
Published: November 2005

Experimental pulse techniques have been developed to verify directly the existence of creeping or circumferential waves that arise from theoretical diffraction theory as developed mathematically by the Watson transformation acoustic step pulses and sine-burst pulses of varying duration and frequency, produced by a transducer using modulation of an ion cloud, are scattered from a rigid sphere in air. The detection transducers, positioned near to and imbedded in the surface of the scatterer, yield measurements of both the amplitude attenuation and velocity of the creeping wave recorded by high-speed, multitrace oscilloscope techniques in conjunction with sample/hold digital data storage. Electronic gating circuits switch the transducers on and off individually or in coincidence as the pulse front advance. The transducers are synchronized in tandem with the pretrigger, trigger, and delayed trigger circuitry of six independent oscilloscope traces. [This work was supported by the U. S. Navy, Office of Naval Research.]
Asymmetries in Cylindrical Waveguides
Authors: Forristall G. Z. , Ingram J. D.
Published: November 2005

Cylindrical geometries with axial symmetry are often used to model physical systems. Although such a model materially simplifies calculations, it may ignore significant effects arising from small asymmetries in the system. In order to demonstrate this and to examine the nature of such effects, a model was analyzed consisting of a cylindrical waveguide with perfectly reflecting walls and an isolated point source displaced a small distance from the axis of the hole. The subsequent analysis shows two distinct types of arrivals associated with the geometry. Both of these produce strikingly large asymmetries in the motion of the system. These effects are clearly displayed in the closed-form solutions obtained for the problem, and the light that they shed on the nature of the reflection process at a cylindrical interface may well be of significant value for ray theory methods in diffraction.
The Morphology of Auditory Neurons and Auditory Localization
Authors: Harrison J. M.
Published: November 2005

The mammalian auditory system of the brain stem contains a number of classes of nerve cells the morphology of which may be relevant to the binaural localization of sounds. The axons of the acoustic nerve give rise to large synaptic endings (bulbs of Held) on the cell bodies of two types o[ nerve cells (types c and g) of the cochlear nucleus. The size of these endings suggests that they dominate the firing patterns of the postsynaptic cells, preserving in them the temporal characteristics of the activity in the acoustic nerve fibers. The medial superior olivary (mso) nucleus contains horizontally oriented bipolar nerve cells whose lateral dendrites probably receive synaptic endings from contralateral type c cells. Their bilateral innervation from cells that are synaptically dominated by the acoustic nerve fibers has suggested that the cells of the mso are of significance in the location of sounds. The medial nucleus of the trapezoid body contains nerve cells each of which is innervated by a single massive synaptic ending (chalice of Held) from large axons of the contralateral type g cells. This would appear to be a rapidly conducting system in which temporal characteristics of acoustic nerve activity may be preserved. The number of nerve cells in the major nuclei of the superior olivary complex varies across mammalian species. The mso varies from 0 (bats and dolphin) to 4200 (cat) nerve cells. The absence of this nucleus in the echolocating bats and dolphin shows that this is not an essential structure for sound localization in mammals. The lateral superior olivary nucleus is well developed in bats (4300) and dolphin and is also present in all species we have examined. This suggests that this nucleus is involved in auditory localization and complex auditory discriminations. The medial nucleus of the trapezoid body is well developed (2100–5800 nerve cells) in all species examined.
On Listening to Competing Stimuli and Functional Differentiation of the Cerebral Hemispheres
Authors: Shankweiler Donald
Published: November 2005

A number of experiments have indicated a reliable right-ear advantage in recognition of speech materials presented dichotically to the two ears. If the stimuli are melodic patterns, however, listeners recognize more accurately those presented to the left ear. Since each ear has greater representation in the opposite cerebral hemisphere, these lateral differences in perception must reflect functional differences between the hemispheres in processing speech and nonspeech stimuli. The special relation of the left cerebral hemisphere to language processes has long been recognized, but the details of this relationship have remained obscure, partly because the evidence could only be obtained through study of patients who had incurred brain damage. The technique of dichotic listening offers an approach to the further specification of the functions of the two cerebral hemispheres in persons with intact nervous systems. Experiments with speech materials are described that bear on the problem of the units of perception and the procedures by which the perceptual apparatus arrives at phonemic decisions.
Adaptive Antenna Systems
Authors: Widrow B. , Mantey P. , Griffiths L. , Goode B.
Published: November 2005

A system consisting of an antenna array and an adaptive processor can perform filtering in both the space and frequency domains, thus reducing the sensitivity of the signal-receiving system to interfering directional noise sources. Variable weights of a signal processor can be automatically adjusted by a simple adaptive technique based on the least-mean-squares (LMS) algorithm. During the adaptive process an injected pilot signal simulates a received signal from a desired “look” direction. This allows the array to be “trained” so that its directivity pattern has a main lobe in the previously specified look direction. At the same time, the array processing system can reject any incident noises, whose directions of propagation are different from the desired look direction, by forming appropriate nulls in the antenna directivity pattern. The array adapts itself to form a main lobe, with its direction and bandwidth determined by the pilot signal, and to reject signals or noises occurring outside the main lobe as well as possible in the minimum mean-square error sense. Several examples illustrate the convergence of the LMS adaptation procedure to the corresponding Wiener-optimum solutions. Rates of adaptation and misadjustments of the solutions are predicted theoretically and checked experimentally. Substantial reductions in noise reception are demonstrated in computer-simulated experiments. The techniques described in this paper are applicable to signal-receiving arrays for use over a wide range of frequencies.