bluuebunny/crossref_metadata_2025 huggingface dataset:
Impedance Changes during Surgery
Authors: Sweitzer R. S.
Published: September 2005

Investigations have shown that the anesthetic agent, nitrous oxide, produces temporary pressure increases in the middle ear. The present study investigated impedance changes during surgery, as measured with a Zwislocki acoustic bridge. Nitrous oxide and halothane were used as anesthetic agents. A control group was administered oxygen. For the experimental groups, measures were obtained before, during, and following surgery. For the control group, measures were obtained before, during, and after the administration of oxygen. Impedance values were obtained for resistance and reactance at 250 and 1000 cps. Analyses of variance were performed on the logarithmic transformation of the original data, in acoustic ohms. It was of interest as to whether or not there were differences between the administration of nitrous oxide under pressure and under no pressure (intubated). Although there were significant differences among the preoperative, during, the postoperative measures, there were no significant differences between the method of administration. The second analysis revealed that, although all agents produced an increased impedance during administration, the nitrous oxide group tended to show the greatest change.
Special Problems in Composite Amplifier-Transducer-Array Behavior
Authors: Porter David T.
Published: September 2005

A general method for computing the electrical and acoustical behavior for a transmitting array is given as an introduction to a discussion of three special problems. The problem of the array with more than one type of transducer in it is presented. To solve this problem, the mutual impedance coefficients between radiators of unequal face area are usually needed. A formula for the mutual impedance coefficients between two circular pistons of unequal radius is given. Another special problem in array analysis occurs when each amplifier drives more than one transducer. This problem is solved by a rapidly convergent iterative procedure. The third problem discussed is the computation of velocities for very large arrays, where the usual method of solution by matrix inversion is not feasible because of computer time or storage. Under some conditions, the velocities can be computed by a method that involves dividing the array into overlapping patches. The size of the array for which the computation can be done can also be increased by solving for the velocities by iteration rather than direct inversion. The convergence of this iterative procedure is related to the transient time for the array.
Continuous Distributions of Dislocations and Energy Dissipation of Metals
Authors: Mura T. , Lyons W. C.
Published: September 2005

The theory of continuous distribution of oscillating dislocations has been joined with Zener's thermoelastic effects to give a possible estimate of the energy dissipation in metals. This approach to the question of energy dissipation was considered first by Eshelby. In this work, Eshelby made the following simplifying approximations: the inertia of the material was neglected, the interaction effect between the dislocations was not considered, and the inside of the dislocation core was not considered, only the medium outside the dislocation bounded by a “cutoff” length l was considered. Also, difficulties appeared in Eshelby's work because of the singularity of the stress field at the center of a dislocation. With the above restricting assumptions Eshelby was able to obtain that the energy dissipation should increase with frequency. This result disagrees with the limited experimental data available. We attempt to improve upon the basic thesis proposed by Eshelby by considering a continuous distribution of dislocations instead of a discrete dislocation. Also, the inertia of the material is included in the analysis.
Damping of Dislocations in Lead Single Crystals
Authors: Mason Warren P. , Rosenburg Arthur
Published: September 2005

Measurements have been made of the attenuation of longitudinal waves along the 〈110〉 direction in a lead single crystal over a frequency range from 30 to 150 Mc/sec and in a temperature range from 60° to 300°K. The attenuation can be divided into a square-law frequency term and a term consistent with the theoretical form of dislocation attenuation at high frequencies. By determining the high-frequency asymptote of the dislocation internal friction and by assuming a reasonable dislocation density, the drag coefficient for the dislocations can be evaluated. The measurements are consistent with the sum of a phonon scattering term and a phonon viscosity term. The square-law attenuation is about twice as large as the thermoelastic loss and over a temperature range is in agreement with the sum of a thermoelastic loss plus a phonon viscosity loss. [Research performed under contract from the U. S. Office of Naval Research with the Institute for the Study of Fatigue and Reliability, Columbia University.]
Measurement of Ultrasonic Intensity in Liquids by Acoustic Measurements in Overlying Air
Authors: Piercy J. E. , Shaw E. A. G.
Published: September 2005

Direct probing of ultrasonic fields in liquid systems of interest to industry are difficult for two reasons: (a) modification of acoustic field by cavitation at probe surface, (b) physical or chemical interaction between probe and medium (e.g., hot molten metal). The sound-pressure level in an air space above the liquid provides a direct but noninteracting measure of the particle velocity of the liquid surface. For an extended sound field in linear media, the ratio of the SPL in the air to that in the liquid has been calculated to be A(Zl/Za), where Z is the acoustic impedance of the medium and A is a constant in the range 0.8–1.4, depending on the field geometry. A probe-tube condenser suitable for such air measurements has been constructed. The dependence of the SPL ratio on Zl has been tested, using a narrow liquid column (water or mercury) coupled to a short air-filled horn. The dependence on field geometry has been tested by measurements also with an ultrasonic cleaning bath.
Ultrasonic Relaxation Caused by Internal Rotation in the Normal Paraffins
Authors: Piercy J. E. , Seshagiri Rao M. G.
Published: September 2005

The ultrasonic velocity and absorption of liquid normal propane, butane, pentane, and hexane have been measured at frequencies of 5, 15, and 45 Mcs in the temperature range −130° to +30°C. In butane, pentane, and hexane, the absorption becomes large and dependent on frequency below −80°C. Measurement of the absorption of a mixture of pentane and propane indicates an intramolecular mechanism, for which the obvious choice is internal rotation about a central carbon-carbon bond. Assuming a single relaxation process, a value of 2.4±0.6 kcal/mole has been derived for the barrier to internal rotation within the butane molecule from the gauche to the trans configuration. Barriers of approximately the same size are indicated for pentane and hexane.
Propagation of Sound in an Aerosol
Authors: Dobbins Richard A. , Temkin Samuel
Published: September 2005

Sound attenuation and dispersion by small, dense particles suspended in a gas are studied analytically and experimentally. A theory for attenuation and dispersion based on particulate relaxation processes is given. The close relationship between particulate relaxation and relaxation mechanisms due to lagging molecular or atomic internal degrees of freedom is displayed. The particulate relaxation theory predicts attenuation and dispersion, in close agreement with existing, more-detailed theories in the vicinity of ωτd=1, where the attenuation per unit wavelength is a maximum (ω is the circular frequency, τd is the dynamic relaxation time of the particles). The experimental study consists of measurements of attenuation and dispersion in an acoustic interferometer. The interference tube is filled with an aerosol composed of oleic acid particles in nitrogen. Particle size and concentration are measured in situ by spectrophotometric tests. Dispersion measurements, taken at low values of ωτd where no previous measurements have been made, indicate good agreement with the theory. Attenuation measurements taken in the range of ωτd from 0.1 to 4.0 show good agreement with the theory. In particular, they confirm the existence of the predicted maximum. [Work supported by the Power Branch of the U. S. Office of Naval Research.]
Measuremenut of the Attenuation Constant in an Acoustic Tube
Authors: Rogers Joseph Wood
Published: September 2005

The theory of a new method for measuring the attenuation constant in an acoustic tube of uniform cross section is described. The idea uses frequency as an independent variable and requires no moving parts. A plot of the ratio of the voltages from the amplifiers of two microphones as a function of frequency is sufficient data. The attenuation constant is found to be 2π⋅Δf/c, in which Δf is a frequency difference determined from the plot and c is the speed of sound in the tube. Apparatus is very simple. Experiments can be performed using two inexpensive microphones and amplifiers, an earphone, a wave analyzer (for filtering extraneous signals), an electronic counter, and some other simple home-made equipment. Some of the experimental difficulties are discussed, with methods for their elimination. The experimental procedure is very simple to carry out.
Measurement of the Early Reflections in Concert Halls
Authors: Delsasso L. P.
Published: September 2005

Measurements of the early reflections and decay of sound from explosive sources have been made in representative concert halls, including the Liederhalle in Stuttgart, the Festspielhaus in Salzburg, and the recently completed Grady Gammage Memorial Auditorium in Tempe, Arizona. Because of the unique acoustical design of the Grady Gammage Auditorium, involving exceptionally large convex cylindrical splays for the walls and ceiling and a balcony detached from the rear wall, detailed acoustical studies were undertaken. Decay records were obtained utilizing white noise, music, and explosive sources. Steady-state white noise in half-octave bands was recorded with a slowly moving microphone. These observations reveal that the auditorium has a remarkably uniform steady state and impulsive response throughout the entire seating area.
Masking-Level Differences with Continuous and Burst Masking Noise
Authors: McFadden Dennis
Published: September 2005

Psychometric functions were obtained for several interaural phase combinations with both continuous and burst masking noise. In the burst conditions, the signal (400 cps, 125 msec) and the wide-band masker (45 dB/cycle) were gated simultaneously; in the continuous conditions, only the signal was gated. Performance on burst N0-S0 was only about 0.5 dB worse than on continuous N0-S0, but the masking-level differences (MLD's) for N0-Sπ, Nπ-S0, N0-Sm, and Nπ-Sm were 4–6 dB smaller with burst than with continuous noise. In an additional experiment, the noise burst (N0) was gated 0, 75, 150, 250, 400, 600, and 1000 msec before the onset of the signal (Sπ). These MLD's increased gradually between 0 and 600 msec and then leveled off at approximately the value obtained with a continuous masker. A single-interval, yes-no procedure was used in these experiments. When two-alternative, forced choice was used, the difference between continuous and burst noise was considerably diminished. [Research supported by the U. S. Air Force Office of Scientific Research and by the Public Health Service, U. S. Department of Health, Education, and Welfare.]
Psychometric Functions for the Antiphasic Binaural Conditions N0Sπ and NπS0
Authors: Evans Rand B. , Tucker Ann , Jeffress Lloyd A.
Published: September 2005

Psychometric functions for N0Sπ and NπS0 were determined, using a 2AFC procedure. The signal was a 500-Hz, 150-msec tone, and the masker, a continuous wide-band noise (100–3000 Hz). The function for NπS0 showed the bend at high levels reported earlier [L. A. Jeffress and A. D. Gaston, Jr., J. Acoust. Soc. Am. 38, 929(A) (1965)] for measured interaural time differences. The function for N0Sπ was similar to that described by Green [J. Acoust. Soc. Am. (to be published)]. [Work supported through a contract with Bureau of Ships and a grant from the National Aeronautics and Space Administration.]
Binaural Thresholds of Pulsive Signals and Place of Detection on the Basilar Membrane
Authors: Flanagan J. L. , Watson B. J.
Published: September 2005

Absolute and masked binaural thresholds are measured for an ensemble of pulsive periodic signals. Spectral composition, interaural time, and pulse rate are signal parameters. Broad-band, interaurally in-phase noise is the masker. From threshold behavior and from masking-level differences (MLD's), evidence is deduced concerning place of detection on the basilar membrane. The experimental observations are supported by calculations of root-mean-square signal-to-noise displacement along the membrane, using Flanagan's model for membrane motion. A typical result of the study shows that a periodic train of unipolar impulses, produced at a rate of 250 pps, has (1) an absolute threshold determined by motion near the 1000- to 2000-cps region of the membrane; (2) an homophasic masked threshold determined by motion near the 250- to 600-cps region of the membrane; and (3) an MLD (or homoheterophasic threshold difference) determined by the spectral presence of the fundamental component. In particular, the findings provide further information about the peripheral processing involved in binaural detection of complex signals.
Crosscorrelation Model for Binaural Unmasking
Authors: Sondhi Man Mohan
Published: September 2005

A model for predicting binaural release from masking is described. The model utilizes peripheral filtering followed by nonlinear distortion and short-time crosscorrelation of left and right signals. A comparison is made of the predictions of the model with measurements from a number of binaural experiments.
Binaural Masking-Level Differences and Improvements in Intelligibility
Authors: Levitt H. , Rabiner L. R.
Published: September 2005

A binaural intelligibility-level difference (BILD) is defined as the difference in signal level (in decibels) between two binaural conditions for a given percent intelligibility. Similarly, a binaural masking-level difference (BMLD) is defined as the difference in masked threshold between two binaural conditions. Using the homophasic S0N0 condition as reference, a BMLD of roughly 13 dB has been observed for speech in broad-band, Gaussian noise at a spectral level of 49.5 dB. The release from masking is determined primarily by interaural phase differences in the low-frequency region near 300 cps. The corresponding BILD for 50% intelligibility is about 6 dB and only partly dependent on low-frequency interaural differences. A simple, approximate procedure for predicting BILD's using BMLD data and the articulation index has been developed. Predictions based on this theory indicate that the relative importance of low- and high-frequency interaural phase differences in producing a BILD depends on the percent intelligibility.
Some Properties of the Vector Model for Binaural Hearing
Authors: Levitt H. , Lundry E. A.
Published: September 2005

The cumulative probability distribution of the phase angle between the left- and right-ear resultant vectors in the binaural vector model has been derived for the S0Nπ and SπN0 conditions. The results show that the approximate procedures adopted by Jeffress et al. [J. Acoust. Soc. Am. 28, 416–426 (1956)] and Webster [J. Acoust. Soc. Am. 23, 452–462 (1951)] are reasonably accurate under certain conditions. A relatively simple, approximate expression for the amplitude distribution of the resultant vector (the sum of a fixed and a Rayleigh-distributed vector) has also been derived. Predictions of BMLD using this model are critically dependent on the internal noise. If the effect of the internal noise is specified in terms of the limited resolution of the binaural system in detecting interaural time differences, then the resolution is found to be relatively constant in the region from 500 to 1400 cps, but to decrease rapidly (i.e., less resolution) for low frequencies. For frequencies above 1400 cps, it is necessary to specify another mode of detection.
Critical Band in Binaural Detection
Authors: Mulligan B. E. , Mulligan M. J.
Published: September 2005

The release from masking obtained by adding a tone at one of two ears which contain correlated noise, or by reversing the phase of the tone at both ears, has been explained in terms of the critical band. The idea is that the ear acts like a sharply tuned filter with a passband that varies as a function of its center frequency. At frequencies below 2000 cps, the width of the passband is narrow. The waveforms of narrow bands of noise approach the regularity of sinusoids, varying slowly in amplitude and phase, as bandwidth is reduced. It has been hypothesized that the critical band is such a band of noise. If correlated noise is presented at the two ears, the sinusoidlike waveforms of the noise within the critical bands are in phase. Consequently, the addition of a tone at one ear results in a phase shift between the two bands. Or, if the tone is at both ears and is masked, reversal of its phase triggers the phase shift between critical bands. It is this interaural phase shift that is thought to account for binaural release from masking. Experiments are reported that confirm the critical-band hypothesis. Removal of the critical-band noise at one ear eliminates the effects of a tone added in the band at the other ear. On the other hand, a very narrow band of noise is sufficient to obtain an interaural phase shift.
Intensity Effects on the Perception of Competing Messages
Authors: Katz Jack , Lucas Charles S. , Olroyd Marie H.
Published: September 2005

Twelve normal hearers were evaluated with a competing letter test. Letters B, C, D, G, etc., or F, L, M, etc., were presented in rhyming pairs, with one letter going to each ear. In the initial experiment, speech was delivered to one ear at a constant (20 dB SL) level while the speech intensity in the opposite ear was increased from 10 to 70 dB. The performance score in the variable ear increased in percent correct up to about 94% at 40 dB. The performance in the constant ear deteriorated as the opposite ear improved. When the intensity of the variable ear reached the 50-dB level, the curve of the constant ear leveled off at about 30%. At the 60 dB level in the variable ear, both ears improved. At 70 dB, performance was reduced bilaterally. In order to rule out the possibility of a “60-dB mechanism” in the auditory system, a second group of 12 subjects was tested with the constant ear at 30 dB and the variable ear increasing from 20 to 80 dB. In this experiment, the peak improvement in the constant ear was obvious at 70 dB instead of 60 dB, as observed in the 20-dB condition. Another experiment demonstrated that the peak improvement in the constant ear occurred at a level 36–38 dB below the intensity of the variable ear.
Pitch Discrimination of Pulse-Train Bursts
Authors: Rosenberg Aaron E.
Published: September 2005

The present study has been designed to investigate the discrimination of pulse-train bursts with respect to the patterns of pulse polarities of the bursts. Listeners are presented with pairs of stimuli consisting of periodically repeated pulse-train bursts. Each pulse-train burst consists of two, three, or four short, equal-amplitude pulses spaced at equal intervals of either 10 or 15 msec. For each member of a stimulus pair, all experimental parameters are identical, except for the polarity patterns. The stimuli of a pair are discriminated on the basis of pitch or timbre and the results indicate that the magnitude of the pitch difference is reasonably correlated with the magnitude of the difference in the number of polarity transitions between the stimuli. That is, discrimination is greatest when the magnitude of this difference is greatest. In addition, it has been observed that discrimination is weaker for lower repetition rates and/or greater pulse intervals, and is generally eliminated with the addition of 350- to 800-cps bandpass noise to the stimuli. It is suggested that the basic pitch percept in these stimuli is time-separation pitch and that discrimination among stimuli can best be explained by differences in temporal patterns of neural volleys rather than by spectral correlates.
Correlation Detection Arrays Designed for Directional Noise Fields
Authors: Tack D. H.
Published: September 2005

Likelihood ratio detectors (having the structure of cross- and auto-correlation receivers) designed for binary detection of directional signals in directional noise fields with transducer arrays are investigated. They have structures similar to detectors designed for isotropic noise [F. Bryn, J. Acoust. Soc. Am. 34, 289–297 (1962)]: e.g., in incoherent detection, the array output data vector is operated on by a linear regression matrix filter prior to array phasing, summation, and square-law detection. For directional noise fields, however, the regression coefficients are weighted time-shift operators and the residual of the output from the pth element is formed with respect to the delayed outputs of all other elements q, where the delays τpq yield maxima of the interelement space-time noise correlation ρpq(τpq). Given sufficient trace velocity diversity between signal and noise across the array, these detectors can outperform standard summation array detectors at all frequencies in a directional noise field, rather than just at low frequencies as is the case for isotropic noise fields. Optimum array geometries (ignoring beam-forming requirements) are linear for directional noise fields. Detector performance is illustrated for an N-element array at a turbulent boundary layer. [The support of the National Aeronautics and Space Administration and the National Science Foundation for this study is acknowledged.]
Array Gain for the Case of Horizontal Noise
Authors: Shaffer Robert L. , Cron Benjamin F.
Published: September 2005

Array-gain computations based on spatial correlation measurements in the (200–400)-cps band and are the directionality of the noise field for center frequencies of 112 and 178 cps are obtained. Both sets of measurements indicate more noise from the horizontal than from overhead at low frequencies, whereas the opposite is true at higher frequencies. The results derived from spatial correlation measurements are compared with theoretical values for a directional noise field and vertical receivers, and the influence of sea conditions on the gain is demonstrated. For all element spacings of the 8-element array and all sea conditions considered, the gain varied from a low of 5 dB to a high of 12.5 dB. A value of 9 dB from the rule-of-thumb 10 log10 N, where N is the number of elements, is obtained for array gain. The results based on directionality of the noise field are below those based on spatial correlation, and the same trend with increasing wind speed is observed. The data for this calculation were available only for the upper half-plane.
Optimum Transmit Patterns for a Clipper-Correlator System in Reverberation and Noise
Authors: Liggett W. S.
Published: September 2005

When a split-beam, clipper-correlator receiver is used in an active sonar system, the mean output may be significantly different from zero even in the absence of an echo owing to the directivity (or correlation) of the reverberation. In this paper, we adopt a model of volume reverberation that allows us to predict the correlation between the unshaded sum beam outputs of the two halves of a uniformly spaced line array in terms of the transmit pattern of the same array with shading. We use this model to find transmit shadings that reduce the reverberation correlation to zero. Upon applying this theory to a 6-element array, we find that zero correlation is achieved with a transmit pattern that is broader than the pattern of the unshaded array. When the reverberation power is much higher than the ambient and self-noise power, the difference between the mean output for echo plus noise and that for noise alone is greater for a broad transmit beam that gives zero reverberation correlation than for an unshaded array.
Ultrasonic Radiation Field of a Focusing Spherical Source at Finite Amplitudes
Authors: Smith C. W. , Beyer Robert T.
Published: September 2005

A PZT-4 ceramic spherical segment with a radius of curvature of 30 cm has been used to produce a finite-amplitude ultrasonic field in water at a frequency of 2.2 Mcps. The field has been observed by a nonresonant probe with an active face of 18 in. diameter. The radiation field differs from that expected from an unbounded source since edge effects are present. This was noted for the low-amplitude case by A. O. Williams, Jr. [J. Acoust. Soc. Am. 17, 219–227 (1946)] and H. T. O'Neil [J. Acoust. Soc. Am. 21, 516–526 (1949)], who showed that the axial values of pressure amplitude from a spherical segment resembled those from a plane piston that is modulated by a reciprocal r term. Harmonic-radiation patterns for the fundamental component in the finite-amplitude case were found in general to be similar to those for the infinitesimal case, but differed somewhat in detail. The higher harmonic have also been measured both along the beam and transverse to it, and some interesting features have been noted. [Work supported by the U. S. Office of Naval Research.]
Radiation-Induced Ultrasonic Cavitation
Authors: Greenspan Martin , Tschiegg Carl E.
Published: September 2005

Working with a cylindrical resonator we find the acoustic cavitation threshold of several liquids to rise as more of the “motes” are removed, with no limit in sight. Exposure to high-energy neutrons yields a reproducible threshold if the liquid is clean enough. The cavitation rate rises sharply with stress, and at a fixed stress is proportional to neutron flux. The events are random. No appreciable induction or decay times are observed, even in water. It is difficult to clean water (strong) so that it sustains stresses >10 dB above neutron threshold, but easy for isopropanol (weak). “Freon TF” (F2Cl C C Cl2F) has a very low neutron threshold and sustains pressures >18 dB above it (neutrons absent). Isopropanol with a dissolved thorium salt exhibits the same sharp neutron threshold, a well-defined α-particle threshold about 5 dB higher, and a poorly defined fast-fission threshold >10 dB lower. All results were obtained at 20–50 kHz and were largely independent of dissolved gas content. [Work supported in part by the U. S. Office of Naval Research.]
Airblasts from Shallow Underwater Explosions
Authors: Malme Charles I. , Carbonell Jaime R. , Dyer Ira
Published: September 2005

A shallow underwater explosion causes a supersonic plume to rise into the air. The plume shockwave produces the major peak in the ensuing airblast signature. An experimental investigation of the interaction between water motion and gas was conducted, wherein the parameters of the gas above the explosion were varied. Helium and “freon-114” were substituted for air, giving a variation of 8 to 1 in sound speed and about 1 to 5 in specific acoustic impedance. The dominant parameter in determining whether the explosion is considered shallow or deep proves to be the Mach number of the plume motion with respect to the gas. Plume velocity, though correlated with gas density, is not inversely proportional to it: a 42-fold increase in density resulted in halving the plume velocity. Some results of a calculation method to predict off-axis airblasts from shallow explosions are also presented. These calculations, which show good agreement with experimental data, consider the plume as a decelerating supersonic blunt body that generates a shock wave. [Research supported by the U. S. Naval Ordnance Laboratory.]
Mechanical Impedance and Mobility Concept
Authors: O'Hara George J.
Published: September 2005

It is the purpose of this paper to discuss the fundamental concepts involved in mechanical impedance and mobility. The equations used in the formulation of the concepts are examined as to meaning and content. It is demonstrated for any prescribed structure that every possible observed mobility element is independent of the number and location of the other measurement points and very possible observed mechanical-impedance element is not. The effects upon the mobility and impedance arrays are discussed for simple expansions and contractions of the tensor. Numerical examples are used to illustrate some of these points.
Recent Advances in the Measurement of Structural Rotational Impedance
Authors: Desiderati Frank W.
Published: September 2005

A technique and instrumentation has been developed to make rotational-impedance measurements on structures. The instrumentation employing two impedance heads, vibration generators, differential amplifiers, and automatic recording equipment is discussed. A simple-calibration procedure has been established and automatic measurements from 20 to 5000 Hz have been performed on a rectangular beam, with varying spacings between the transducers, showing the effects of local deformation and coupling between translational and rotational modes for small spacings.
Structural Characterization of Mechanical-Impedance Techniques
Authors: Tatge R. B.
Published: September 2005

In present-day practice, the decision as to whether a device has suffered damage as a result of exposure to a severe environment is generally based on operability during and after exposure, and visual inspection. Since these measurements do not necessarily disclose the presence of mechanical faults, particularly in field units, a need exists for a purely structural test to tell if a failure has occurred. Mechanical-impedance techniques offer an opportunity for structural characterization to determine whether a device conforms to a predetermined standard or has suffered a change as a result of its history. From reference to network theory, it can be shown that changes in the resonant and antiresonant frequencies are sensitive indicators of change in a structure; these have the advantage of being relatively easy to measure with accuracy. The time that the structure must be excited in order to make the necessary measurements for such a test can be minimized by using random-noise rather than swept-sine excitation. With proper instrumentation the results obtained with the two are equivalent.
Influence of Distortion Components upon Word Intelligibility
Authors: Corliss Edith L. R. , Burnett E. D. , Bassin M. A.
Published: September 2005

Word lists of the CNC type were recorded on tape via a technique described by Burnett [J. Acoust. Soc. Am. 34, 1997(A), (1962)] that permitted generation of a distorted signal on a second track simultaneous with the linear signal. In Burnett's technique, the signal to be recorded was first passed through a 90° phase splitter and then the distorted signal was obtained by squaring the output. The squaring process applied to the 90° shifted signal produced a phase shift of 180°, so that various of the distortion components could be canceled or enhanced by combining the squared signals from the output of the splitter. By attenuation between the linear and distorted tracks, a number of mixtures of linear and distorted speech could be obtained. The distortion process that enhanced the components most nearly harmonically related to the linear speech signal proved least destructive of intelligibility. The process that enhanced the difference-frequency intermodulation components was decidedly more efficient in reducing intelligibility, but—unexpectedly—the distorted signal produced by squaring alone without cancellation was most damaging to intelligibility. It appears that the ear is confused by the number of components as well as their magnitudes. [Work supported in part by the Veterans Administration.]
Homonyms within the Set of Monosyllabic English Words
Authors: Bhimani B. V. , Mitchell R.
Published: September 2005

The existence and implications of large sets of homonyms within the set of elementary English words have been discussed in earlier papers [B. V. Bhimani, L. Earl, and R. Mitchell, J. Acoust. Soc. Am. 37, 1210(A) (1965); B. V. Bhimani, ibid. 37, 1210(A) (1965)]. The work has now been extended to include the set of lexed items monosyllabic according to the Shorter Oxford Dictionary. Some operational approaches to the resolution of homonyms are discussed. Because of the wide variation in the number of homonyms according to each of the five dictionaries studied, the effect of dialects was considered, together with (a) information on parts of speech of the lexed items and (b) the status of the items in the dictionaries as “current” or “obsolete.” [Work supported by Lockheed Independent Research.]
Plane-Wave Interaction with Time-Varying Ocean Surface
Authors: Hayre H. S.
Published: September 2005

Considerable work has been done in the field of tinlc-variant modeling of ocean surface using one-dimensional, two-dimensional, and isotropic rough surfaces. Usually, the surface-height roughness in each direction is assumed. The author has previously shown that a single random variable, such as waveheight cannot adequately characterize the scattering of plane waves by such a surface. Furthermore, it was also demonstrated that a small-scale and a large-scale roughness model yields very satisfactory theoretical results, and, in particular, brings out the significance of the crosscorrelation term between these two random variables. As an extension of this time-invariant analysis, the University of Houston Department of Electrical Engineering is conducting both theoretical and experimental work using a 20-ft-diam water tauk, employing a time-varying water surface. Detailed surface analysis in both time and space is being carried out in conjunction with its surface-scattering characteristics. Analog and digital instrumentation, experimental results, and theoretical analysis are discussed. Detailed discussion about the critical nature of the wave description is also included. [Work sponsored by the U. S. Office of Naval Research.]
Fine Structure of Scattered Acoustic Fields
Authors: Hurdle Burton G.
Published: September 2005

Extending previously reported work [“Effect of Transducer Velocity on the Structure of Signals Scattered from the Ocean Bottom,” J. Acoust. Soc. Am. 36, 1936 (1964)], a method for describing the fine structure of acoustic signals scattered from the ocean bottom is presented. The fluctuating characteristic of scattered signals is shown to be the result of intercepting the lobes or the interference field when the source and/or receiver are in motion. Lobe widths computed from measured data are independent of speed and in good agreement with a simple physical model. Lobe widths also appear to be independent of bottom roughness. The similarity of acoustical scattering with optical scattering employing a monochromatic source is discussed.
Sound Reflection from a Low-Velocity Bottom
Authors: Winokur Robert S. , Pascoe Joyce C.
Published: September 2005

Measurements of ocean-bottom reflectivity were made in an area in the Caribbean Sea, using explosive sound sources. Observed bottom-reflection coefficients for various frequencies were determined for grazing angles between 2° and 85°. Theoretical reflection coefficients were computed, using a model that consists of a multilayered ocean bottom in which the lowermost layer is considered to be semiinfinite and solid. The layers are assumed to have plane parallel interfaces and to be absorbing. Sediment sound-speed measurements made on cores collected in the area, and used in the theoretical computations, indicate the ocean bottom in this region to be a low-velocity sediment interspersed with thin high-velocity layers. Oscillograph records made of the bottom-reflected signals show a phase reversal, with respect to the incident wave, at the angles theoretically predicted for the lowvelocity bottom. Comparisons of theoretical and measured reflection coefficients are made and indicate that the model is useful for predicting bottom reflectivity in this area.
Determination of Quantitative Structural Relations in Brain Implemented by Ultrasonic Lesions
Authors: Fry William J.
Published: September 2005

The quantitative determination of nerve-cell populations of brain structures after degeneration of the cell bodies following the placement of appropriate lesions constitutes a powerful method of determining structural relations in brain. The features of the ultrasonic method of lesion production that make it particularly useful in such studies are briefly reviewed, and lesions in specific structures pertinent to the quantitative study of the mammillary complex of cat brain are illustrated. The reproducibility, for the methods presently employed, of neuronpopulation ratios for related structures now under investigation is discussed, and the use of such data to determine neuronal circuitry relations is illustrated by a specific example. This presentation does not require prior neuroanatomic knowledge as a basis for its understanding. Its purpose is to illustrate the principles of deciphering quantitative relations of connections between sets of nerve cells and this can be achieved without prior knowledge of the system to which the methods are applied.
Comparison of Ultrasound Echo Patterns from Livers of Different Species
Authors: Kelly Elizabeth , Okuyama Daitaro , Fry William J. , Leichner Gene H. , Fry Francis J.
Published: September 2005

Ultrasonic pulse echo patterns obtained from livers of different degree of connective tissue density exhibit markedly contrasting characteristics. This is illustrated by comparing pictures of liver cross sections of pig and cat. In the pig, after weaning, connective-tissue structure develops to distinctly define the so called lobules. Ultrasonic visualization of structural features of the pig liver are demonstrated. In other adult mammals, including humans and cats, the connective-tissue sructure is poorly developed. The echo patterns obtained show an absence of the echo density seen in pig liver. In this regard, the patterns resemble those reported by other investigators for healthy human liver. Comparison is made of the echo pattern for the adult pig liver and the patterns appearing in the literature for the cirrhotic human liver. The results reported here were obtained primarily on excised livers and the patterns were studied as a function of time after excision. The pattern for the exposed cat liver with normal blood supply intact was also obtained and compared to that of the excised liver. ]Investigation supported partially by the National Cancer Institute, National Institutes of Health, Public Health Service, U. S. Department of Health, Education, and Welfare.]
Musical Composition with the Computer
Authors: Tenney James
Published: September 2005

A set of composing programs has been written for use in conjunction with M. V. Mathews' “Music IV” sound-generating program. They allow the composer to specify the formal evolution of a composition entirely in terms of time-varying statistical conditions. Stochastic processes are then used to realize these conditions, within a framework of certain principles of musical structure and perception derived from the early gestalt psychologists. Tapes are played.
Effect of Signal Duration on Detection for an Electrical Model
Authors: Jeffress Lloyd A. , Gaston Audley D.
Published: September 2005

At the November 1965 meeting of the Society [J. Acoust. Soc. Am. 38, 928(A) (1965)], we presented the results of a series of unsuccessful attempts to replicate the findings of Green, Birdsall, and Tanner [J. Acoust. Soc. Am. 29, 523–531 (1957)] on detection versus duration. Since then, still using a fixed-bandwidth filter, but by changing the time constants of the detector, we have come much closer. Like them, we have employed a continuous masker and a constant value of E/No and our new data yield a close fit to theirs. The filter is followed by a linear (half-wave) detector and by an integrator with a decay time of 100 msec. A replication of the experiment, this time employing a square-law rectifier (energy detector), but using the same integration time constants, yielded reasonably similar results. [Work supported through a contract with the U. S. Bureau of Ships and a grant from the National Aeronautics and Space Administration.]
Masking by Continuous and Gated Sinusoids
Authors: Green Dawn M.
Published: September 2005

The detectability of a sinusoidal signal of 1100 sec duration and variable frequency was measured in the presence of a sinusoidal masker. The masker frequency was fixed in power. For a continuous masker, the data agreed essentially with those reported by Wegel and Lane in their classic paper and with the recent studies by Small and by Ehmer. When the masker was gated, it lasted 1100 sec and was simultaneous with the signal. At or near the signal frequency, there was little difference in the amount of masking produced by the two conditions, although gating the masker produced somewhat more masking, about 5 dB. Off frequency, e.g., at 4200 cps with a 3000-cps masker, the gated condition produced substantially more masking, e.g., 25–30 dB. Masking frequencies of 250, 1000, and 3000 cps were studied; somewhat smaller differences occurred at the lower frequencies. [Research supported in part by the National Institutes of Health, Public Health Service, U. S. Department of Health. Education, and Welfare.]
Frequency and Time Uncertainty in Auditory Detection
Authors: Bourbon Walter T. , Hafter Ervin R. , Evans Thomas R.
Published: September 2005

Studies have shown that the detectability of auditory signals is reduced when the observer is uncertain as to the frequency of the signal. Uncertainty as to the time of occurrence of a signal also reduces detectability. Because of the similarities between time and frequency, the effects on detectability of simultaneous uncertainty in the two domains were examined. Frequency uncertainty was varied between the condition in which the same frequency was presented on every signal trial and that in which the frequency was one of seven possible frequencies on any signal trial; those employed were 500, 750, 1000, 1500, 2000, 2500, and 3000 Hz. In the time domain, two procedures were employed: one was the classical fixed interval, yes-no, the other, a variant of the method of free response in which the interstimulus interval varied between 5 and 25 sec. These experiments showed that the losses due to time and frequency uncertainty were not simply additive, suggesting a common factor in the two sources of uncertainty.
Review of the Principal Phenomena of Transient Radiation and Scattering
Authors: Junger M. C.
Published: September 2005

This paper summarizes two basic processes generating acoustic transients: sound radiation by transiently moving solid boundaries and scattering of transient sound pulses by single scatterers. The velocity history of the radiating surface is related to the farfield pressure history in terms of the source geometry. Transients radiated by an impulsively accelerated solid are described. For “pulsed CW” sources, the transition of radiation loading and directivity patterns is traced from the transient to the steady-state régime. Different aspects of the physical process are emphasized by various analytical formulations (wave-harmonic and creeping-wave solutions; Kirchhoff approximation). This correspondence also holds for the scattering problem. The diffraction of a pressure step wave by a finite object is described. The echo structure of a pulsed CW signal is related to pulse-length and scatterer geometry and, for elastic scatterers, to their transient structural response. [Study supported by the U. S. Office of Naval Research and General Dynamics/Electronics.]
Propagation and Reception of Transient Underwater Sounds
Authors: Marsh H. W.
Published: September 2005

Measurements of sound propagating from underwater detonations are described, in terms of waveform and spectra. Correlated analytical results are presented, which emphasize the comparative effects of finite amplitude, relaxation, viscosity, and geometrical spreading. A transient (pressure) is defined to be the event between successive crossings of ambient pressure. The reception and analysis of such transients is discussed.
Acoustic Waves from an Impulsive Source in a Fluid-Filled Borehole
Authors: Rosebaum J. H.
Published: September 2005

Theoretical analyses in terms of radial and circumferential modes as well as rays are presented. Outstanding features of the response are also obtained in closed-form expressions, which are leading terms of asymptotic series. For source or detector near the borehole axis, the first refracted P-arrival decays approximately as 1/(zlog2z), where z is the nondimensional axial source-to-detector distance. The first refracted S arrival is much larger for moderate z, but decays as 1/z2. The relation between the S arrival and the “pseudo-Rayleigh” wave is discussed on the basis of modal theory; a simple description of the “tube wave” in terms of integrals of Airy functions is presented. The existence of a low-frequency “bending wave” may be of interest in noise studies. In the axial-ray picture, the borehole axis is a caustic, where rays are subjected to a 90° phase shift. For the pulse problem, this leads to precursors. The simple theoretical expressions agree with the results of Roever and Vining's model studies, carried out many years ago at the Shell Development Laboratory in Houston.
Transient Detection by Delta Modulation
Authors: Tufts D.
Published: September 2005

Delta modulation is a method of single-bit-per-sample analog-to-digital conversion utilizing feedback around a hard limiter. The digital patterns produced by a delta modulator can be used for transient detection. The results of investigating the value of delta modulation for transient detection are discussed. Both theoretical results and data from experiments by computer simulation are presented. Limited comparison is made with methods based on measuring energy differences. It is assumed that the only information available concerning the transients are nominal ranges for frequency band, duration, and rise and fall times. The waveforms are unknown.
Theoretical Model of Pressure Correlations on the S-IC Vehicle Owing to Exhaust Noise
Authors: Potter R. C.
Published: September 2005

The pressure fluctuations on a rigid cylinder owing to the scattering of an obliquely incident plane acoustic wave have been determined. This result is used to study the correlation pattern of the pressure fluctuations on the S-IC vehicle owing to the noise of the exhaust gas mixing, when the vehicle is at the test or launch stand with the exhaust flow deflected. The plume is replaced by a series of discrete-frequency sources, set at various positions in the exhaust gas, with sources of the whole spectrum of the noise generated occurring in each uncorrelated volume of the exhaust flow. The problems have involved obtaining a correct representation of the uncorrelated nature of the various sources, both in space in the exhaust gas and time for each individual source. Curves of the resultant pressure correlation patterns around the vehicle have been calculated for various frequency bands. [Work supported by NASA-Marshall Space Flight Center, directed through Brown Engineering Company, Huntsville, Alabama.]