bluuebunny/crossref_metadata_2025 huggingface dataset:
Ultrasonic Scattering and Attenuation in Polycrystalline Copper and α-Brass
Authors: Krautkopf David W.
Published: September 2005

The ultrasonic pulse-echo technique has been employed to study scattering and attenuation in polycrystalline copper and α-brass. Specimens in the form of cylindrical rods were annealed to various grain sizes and tested at frequencies between 100 kc and 18 Mc, corresponding to scatterer circumference to wavelength ratios (πD/Λ) from 10−3 to 1.6. The primary objectives of this investigation were to study the scattering process by direct observation of the scattered radiation, and to study the associated attenuation under conditions not previously amenable to measurement; these included cases where pulse patterns were complicated by excessive scattering, and by mode dispersion. A preliminary investigation of the complications attending the propagation of acoustic pulses was performed for steel rods over a range of specimen radius to wavelength ratios (a/Λ) similar to that to be covered in the later work. Pulse patterns were found to be relatively free from complication far a/Λ<0.1, and >10, approximately. In the intermediate range, the distribution of the input energy among the various vibration types was found to vary with a/Λ, and with the details of the excitation. At low a/Λ, (<0.2), where solutions of the Pochhammer frequency equation predict only one mode of vibration for the rod, an additional mode was observed. This made corresponded in timing to a shear mode generated upon reflection of the predicted made, and can be accounted for by considering those roots of the frequency equation corresponding to Bessel functions of imaginary argument. To avoid the complications due to mode dispersion, the scattering experiments were designed to measure critically backscattered radiation, i.e., the scattered sound that arrived at the detector before any of the modes could effect a round trip. The observed scattering levels were in reasonable agreement with theoretical expectations (based on Bhatia's theory for scattering in the long wavelength region), except at low πD/Λ where the backscattering was seen to decrease with increasing frequency. The reason for this discrepancy is not yet definitely established, but it is believed to be a manifestation of propagation phenomena associated with the presence of attenuated vibrations in lossless media. Attenuation measurements were performed with pulses of duration comparable to the length of the specimen. This, combined with the high scattering ability of the medium, results in a pulse pattern whose envelope masks the details of the mode pattern. The rate of decay of this envelope corresponds to the attenuation of scattered sound and hence characterizes the intrinsic absorption properties of the metal. At πD/Λ≈10−1 the energy attenuations were approximately 3×10−3 db/grain for copper and approximately 3×10−4 db/grain for α-brass. Comparison of the experimental data with the principal attenuation mechanisms operative at these frequencies showed the observed attenuation to vary over most of the range in the manner expected for elastic hysteresis damping.
On the Dependence of Directivity Patterns on the Distance from the Emitter
Authors: Pachner Jaroslav
Published: September 2005

A method is developed for easily determining the directivity pattern in an arbitrary distance from the emitter from measured instantaneous values of the field in other distance. Numerical computation is facilitated by the tables put together in this paper.
Investigation of Scalar Wave Fields by Means of Instantaneous Directivity Patterns
Authors: Pachner Jaroslav
Published: September 2005

A method is proposed for determining the traveling and standing components of an arbitrary scalar wave field from the measured instantaneous values of the field on the surface of two spheres surrounding the emitter.
Shock Spectrum Computer for Frequencies up to 2000 cps
Authors: Morrow Charles T. , Riesen Donald E.
Published: September 2005

The shock spectrum for an acceleration impulse applied to an electronic equipment or other component is a measure of severity of mechanical shock in terms of possible peak response at each frequency within the component structure. It is commonly measured by a reed gauge, which is intended to simulate the possible resonant characteristics of the internal structure. The reed gauge is bulky, however, and provides data at a limited number of frequencies.

The shock spectrum computer operates on an accelerometer signal, either direct or recorded, and permits measurement of as many points in the spectrum as desired. It is a device which solves the differential equation of a simple undamped resonant mechanical appendage for any applied impulse of acceleration to yield the response. In the present version, the response is made available as an output signal which is applied to a commercial cathode-ray oscilloscope. Peak accelerations and their time of occurance may be obtained readily from the oscilloscope display. The computer can be tuned to any frequency up to 2000 cps. Control circuitry is used to damp the computer shortly after each impulse and to undamp it immediately before the next so that the impulse under study can be applied repeatedly from a recirculating loop of magnetic tape. Shock spectra obtained from the computer and oscilloscope display are used as a measure of the severity of shocks experienced by electronic apparatus and as a basis for deriving shock specifications for use in design approval tests.
Measurement of the Displacement Distribution of an Ultrasonic Vibrator by Means of Multibeam Interferometry
Authors: Sakurai Takemaro , Shirahase Reiji , Anzai Tarō
Published: September 2005

The displacement distribution of the vibrator of the Langevin type was observed by means of multibeam interferometry. The displacement at various portions of the surface was measured as a shift of the contour fringes. Besides the fundamental mode at 84 kc, several modes of vibration were found between 50 and 400 kc.
Scattering of Impulsive Elastic Waves by a Smooth Convex Cylinder
Authors: Gilbert Freeman
Published: September 2005

The canonical problem of scattering by a circular cylinder is expressed in integral form. The integrals are evaluated asymptotically to yield the first motion approximations. The geometrical theory of diffraction, developed by Keller, is combined with the first motion approximations to solve the problem of scattering by a smooth convex cylinder. The results are valid for pulses whose durations are short compared to the travel time across the cylinder.
Theory of Propagation of Elastic Waves in a Fluid-Saturated Porous Solid. I. Low-Frequency Range
Authors: Biot M. A.
Published: September 2005

A theory is developed for the propagation of stress waves in a porous elastic solid containing compressible viscous fluid. The emphasis of the present treatment is on materials where fluid and solid are of comparable densities as for instance in the case of water-saturated rock. The paper denoted here as Part I is restricted to the lower frequency range where the assumption of Poiseuille flow is valid. The extension to the higher frequencies will be treated in Part II. It is found that the material may be described by four nondimensional parameters and a characteristic frequency. There are two dilatational waves and one rotational wave. The physical interpretation of the result is clarified by treating first the case where the fluid is frictionless. The case of a material containing viscous fluid is then developed and discussed numerically. Phase velocity dispersion curves and attenuation coefficients for the three types of waves are plotted as a function of the frequency for various combinations of the characteristic parameters.
Acoustical Signal Detection in Turbulent Airflow
Authors: Smith M. W. , Lambert R. F.
Published: September 2005

Improvement in detected signal-to-noise ratio is obtained for a periodic signal masked by additive noise and turbulent noise backgrounds. Comparisons are made between autocorrelation, crosscorrelation, and a combination of frequency filtering and crosscorrelation. Although the latter method provided the greatest improvement, the crosscorrelation technique was the most successful single method. It turned out that the maximum improvement obtainable was limited by the dynamic range of the correlator computer and not by errors due to finite averaging time and scanning the delay. The improvement for signals masked by turbulent noise was found to be about 5 db less than that obtained for additive noise.
Digital Array Phasing
Authors: Anderson Victor C.
Published: September 2005

The extension of digital techniques to the problem of processing the output of an array of point receiving elements in an acoustic field has given rise to a method of phasing called DIMUS (digital multibeam steering). This digital technique incorporates the use of shift registers as delay line elements which results in a number of operational advantages. A description of the DIMUS technique is given. The effects of amplitude and time quantization imposed by the digital circuits are considered in the light of the relative signal processing gain of the array referred to an exact analog phasing network. The processing gain is computed as a function of sampling frequency for a number of types of signals.
Small Signal Detection in the DIMUS Array
Authors: Rudnick Philip
Published: September 2005

In the DIMUS system for steering an acoustic array, the output of each element is reduced to a sequence of polarity samples and delayed by an integral multiple of the sampling period. Calculations are given to show the effect of this process on the passive detection threshold of an array beam (in isotropic Gaussian noise) both in general and numerically for several examples. In these, over all losses range from 0.5 to 1.5 db.
Production of Lesions in the Central Nervous System with Focused Ultrasound: A Study of Dosage Factors
Authors: Hueter T. F. , Ballantine H. T. , Cotter W. C.
Published: September 2005

Applications of ultrasonics in neurosurgery involve the production of lesions of a specified size at a specified location, and in a reproducible fashion. Control of the dosage required for a given lesion depends on the geometry of the focal region, the exact determination of focal intensity and the relation between irradiation parameters and biological effect. From an analysis of these factors an optimum frequency for each focal depth is determined and an empirical dosage relationship based on ultrasonically produced paralysis in mice is stated. The mechanism of cell destruction by ultrasound is shown to be a temperature-dependent mechanical effect originating at weak points in the tissue. The difficulties in extrapolating results obtained with experimental animals to applications in human neurosurgery are pointed out.
Diffraction Effects in the Ultrasonic Field of a Piston Source and Their Importance in the Accurate Measurement of Attenuation
Authors: Seki Hajime , Granato Andrew , Truell Rohn
Published: September 2005

A study is made of the ultrasonic field produced by a circular quartz crystal transducer and the integrated response of a quartz crystal receiver with the same dimensions as the transducer. The transducer and receiver are taken to be coaxial, and it is assumed that the transducer behaves as a piston source while the integrated response is proportional to the average pressure over the receiver area. Computations are made for cases of interest in the megacycle frequency range (ka=50 to 1000; a=piston radius; λ=wavelength; k=2π/λ). The results contain features of use in identifying and correcting for diffraction errors. These features which apparently have been missed in previous investigations are compared with available experimental data. Finally correction formulas to account for diffraction effects in the accurate measurement of attenuation are discussed. It is shown that the order of magnitude of the diffraction attenuation is given by one decibel per a2/λ.
Hearing Loss Due to Gun Blast
Authors: Muirhead J. C.
Published: September 2005

A shock wave subjects the ear drum to an oscillatory, rather than a single transient pressure load. It is suggested that the frequency range in which hearing loss due to gun blast occurs is related to the frequency of this pressure oscillation.
Distortion of Finite Amplitude Sound Wave
Authors: Powell Alan
Published: September 2005

A simple, approximate method yielding results of good accuracy is given for finding the time-dependent Fourier components of an initially sinusoidal sound wave of finite amplitude.
Performance of a Type B Fog Horn
Authors: Thiessen G. J.
Published: September 2005

Measurements on a type B fog horn indicate that the nominal frequency of 180 cps is far from any resonance peak in the resistance ratio of the horn. Efficiencies of much less than one percent are therefore commonly encountered. Actual diaphone frequencies in the field range between 180 and 245 cps. The frequency stability with pressure is poor, and large deviations from symmetrical piston movement occur. It can generally be stated that a fog horn that “grunts” is not operating efficiently.
Experimental Study of the Vibrations of a Circular Cylindrical Shell
Authors: Gottenberg W. G.
Published: September 2005

An apparatus is described which permits the mode shape of a vibrating circular cylindrical shell to be obtained quite easily. These measurements are made without contacting the cylinder and can be converted to actual lineal values. A representative number of results obtained with such a system are shown to illustrate the relationship between the nodal pattern and frequency in a cylinder as well as the effect of internal pressure on these frequencies. Finally, comparisons are made between these results and Timoshenko theory and an appropriate shell theory.
Shallow Water Under-Ice Acoustics in Barrow Strait
Authors: Milne Allen R.
Published: September 2005

During April and May 1959, some underwater acoustic measurements were made in Barrow Strait in the Canadian Arctic Archipelago. The water in the experimental area was covered with 7 ft of young, shore-fast ice and depths ranged between 380 and 815 ft.

Recordings of ambient noise were made at one location to include frequencies between 3 cps and 10 kc. These exhibited several harmonically related spectrum lines and, in particular, a prominent line near 7 cps which appeared to have a wind-induced excitation. The frequencies of the spectrum lines are apparently related to a set of standing waves between the surface and the bottom of the water. No relation between the frequency of the air-coupled flexural wave in the ice (17.5 cps) and the ambient noise spectrum was detected.

The velocity of sound vs depth in the water had a mean positive gradient of 0.04 sec−1, caused primarily by a positive temperature gradient. The velocity of sound vs depth in the sedimentary column, obtained by seismic refraction methods, can be expressed as 9025–4300 exp (−z/300) ft/sec with z in feet.

Additional work included a sound transmission run to a range of 10 nautical miles (hereafter abbreviated-nm) using explosive charges as sources. At distant ranges the transmission loss was essentially that to be expected from cylindrical spreading but exceeded this by 1 db per nm in the 9.6 to 19.0 kc band.
Axially Symmetric Vibrations of a Thick Cylindrical Shell in an Acoustic Medium
Authors: Greenspon Joshua E.
Published: September 2005

This paper treats the dynamic behavior of infinitely long thick cylindrical shells surrounded by water. The shell is excited by axially symmetric forces. The solution is formed by coupling the three-dimensional elastic solution with the expression for the fluid pressure in cylindrical coordinates. Curves are presented which give the forced vibration amplitude and acoustic pressure in the water as a function of frequency for various modes of vibration of the cylinder.
Effect of Repetition on Articulation Scores for PB Words
Authors: Thwing Edward J.
Published: September 2005

Naive listeners were administered PB word articulation tests under four conditions of successive repetition and three conditions of signal-to-noise ratio. At all three signal-to-noise ratios, successive repetition of test words yields slightly higher articulation scores. The major portion of improvement in scores occurs with the second presentation; third and fourth presentations have negligible effect.
Acoustical Features of the Addition to the Physics Building at the University of Texas
Authors: Watson Robert B.
Published: September 2005

Detailed description is given of the acoustic designs used in the addition to the Physics Building at the University of Texas. Sound absorption is included in the lecture rooms in the form of an acoustic blanket behind a pierced glazed brick wall to give a broadly resonant absorption with maximum coefficient at 500 cps of 0.60, reducing to 0.40 at 125 cps and to 0.25 at 4000 cps, and in the form of a slit absorber having a resonance at about 400 cps with coefficient of 0.55, reducing to 0.45 at 125 cps and 0.33 at 4000 cps. Sound diffusion and projection in these lecture rooms is secured by sound reflectors over the speaker's position, nonparallel side walls, and light fixture coves in the ceiling. Sound absorption in some of the laboratories is provided by use of functional absorbers each using an acoustic blanket free on one side and confined by a perforated hardboard on the other. Measurements on two such rooms show a resonant absorption is obtained with peak frequency at 500 cps, and with apparent absorption coefficient near unity at the peak, dropping to 0.70 at 125 cps and to 0.50 at 4000 cps.
Some Notes on the Measurement of Acoustic Impedance
Authors: Mawardi Osman K.
Published: September 2005

The theory for a plane wave method of measurement of acoustic impedance in a tube is worked out. The effect on the measurement of irregularities in the surface of the sample has also been investigated. It is shown that the measured impedance differs from that of the average impedance evaluated at the surface of the specimen. A number of recommendations for the method of preparation of a sample have also been given.
Improved Type B Fog-Horn System using Exponential and Catenoidal Horns
Authors: Thiessen G. J.
Published: September 2005

The use of a high impedance acoustical load for the type B diaphone is capable of raising the efficiency of the fog horn system to values of 10 to 16% for normal operating pressures. The high impedance is provided by a resonant exponential or catenoidal horn. To provide the high degree of frequency stability required by high Q resonant loads the mechanical impedance of the diaphone is reduced to permit it to lock in with the horn frequency. The reduction of the mechanical impedance is achieved by reducing the mass of the piston through the use of aluminum and reducing and stabilizing the frictional forces by using a central shaft for supporting the piston instead of allowing it to float in the liner. The resulting frequency stability is such that the efficiency under field conditions equals that obtained in the laboratory. An incidental benefit arises from the fact that the horns are smaller and made of aluminum reducing the weight by a factor of six.
Fourier Transform Method for the Treatment of the Problem of the Reflection of Radiation from Irregular Surfaces
Authors: Meecham William C.
Published: September 2005

A method is presented which can be used for the calculation of the distribution of energy reflected from irregular surfaces. The formulation is useful for the first boundary value problem and can be used in either two- or three-dimensional problems with any given incident field. The solution is reduced to quadrature with negligible error when the average square of the slope of the reflecting surface is small and when the wavelength of the incident radiation is not small compared with the displacement of the surface from its average value. A numerical example is worked, the sinusoidal surface, and is compared with experiment and with a method due to Rayleigh. It is found that the Fourier transform method is preferable to previous methods, notably those which can be classified physical optics (such as Rayleigh's), since the error in the transform method is of second order in the surface slope whereas the error in previous methods is of first order in the same quantity.
Pressure Fluctuations in Turbulent Flow over a Flat Plate
Authors: Kraichnan Robert H.
Published: September 2005

The pressure fluctuations exerted on a flat plate by a turbulent boundary layer flow are investigated. The approximate dependence of the mean-square intensity, spatial scale, and frequency scale on Mach number and distance from transition point are estimated through the use of similarity arguments. The wave number spectrum of the pressure fluctuation distribution over the surface of the plate is expressed in terms of transforms of two-point velocity correlations and expressions are derived for the driving force exerted on a rectangular piston set in the surface of the plate. It is found that the integral over the boundary surface of the two-point quadratic correlation function of the pressure fluctuation should vanish, with the result that the mean-square force per unit area exerted on a large area of the surface should tend to zero as the area increases indefinitely. An idealized model of turbulent boundary layer flow is constructed and used to relate the spectrum and correlation function of the surface pressure distribution to the corresponding functions for a homogeneous turbulent flow. Application of the theory to Laufer's data on turbulent channel flow indicates that the dominant contribution to the pressure fluctuations should depend only on the mean velocity profile and the two-point quadratic correlation of the fluctuating velocity component perpendicular to the boundary surface. On the basis of the seriously incomplete data available the rms pressure fluctuation from this source is tentatively estimated. The treatment of the present paper is based on the assumptions of (1) adiabatic conditions, (2) small compressibility, and (3) slow rate of growth of the boundary layer.
Ultrasonic Measurement of the Elastic Moduli of Rutile
Authors: Vick Gerald L. , Hollander Lewis E.
Published: September 2005

Four of the elastic moduli of rutile have been determined by measuring the velocity of 10-Mc ultrasonic waves. They are C11equals;2.48±0.08, C33=4.52±0.08, C44=1.20±0.03, and C56=1.6±0.1, all×1012 d/cm2. The remaining two, C12=2.0±0.1×1012 d/cm2 and C13=1.4±0.1×1012 d/cm2, were computed from the given data and Bridgman's compressibility data. These values are, with the exception of C33, in good agreement with values computed from force constant data. No change in elastic moduli was noted upon reduction to a resistivity of 0.2 ohm/cm. It was noted that attenuation was greater in reduced than in fully oxidized rutile and was considerably greater in the a than in the c crystallographic direction.
An Approximate Solution to the Acoustic Radiation of a Finite Cylinder
Authors: Brigham G. A. , Borg M. F.
Published: September 2005

Utilizing the assumption of an omni-directional point source and varying degrees of acoustical transparency associated with a finite cylindrical shell with rigid end caps, the authors have derived two separate approaches to the problem of far-field sound radiation emanating from a normal mode of vibration. In addition, a third approach is obtained by expanding the expressions of Laird and Cohen and applying them to a shell-band source on an infinite cylinder. Several different environments are considered for each approach and for one of these environments, the results are compared to the experiment.

The comparison of these theories indicates that for acoustic wavelengths considerably greater than structural wavelengths and dimensions, the assumption of omni-directional point sources and acoustical transparency is reasonable even though the source is curved and “unbaffled.” At higher frequencies, the pressure levels and directivity in the far field are approximately independent of the transparency or opaqueness of the source, thus indicating that an “equivalent” transparent cylinder of infinitesimal spherical sources could give, at most, only three- or four-db cancellation effects when a single mode excitation basis is assumed.
Aerodynamic Noise and the Plane Boundary
Authors: Powell Alan
Published: September 2005

In an earlier paper entitled “Thoughts on Boundary Layer Noise” (Aeronautical Research Council Report 16727, 1954), it was pointed out that while the fluctuating pressures exerted upon a rigid boundary by a contiguous unsteady flow can be shown in a formal manner to generate sound as of a distribution of dipoles, it can be argued by means of the reflection principle that all such dipole effects cancel out in the case of the boundary being plane; yet observations of aeolian tones adequately confirm the presence of effective dipole-like generators in that case. Here the image principle is developed in a rigorous manner and the apparent paradox is resolved with the help of an extension of Lighthill's and Curle's analyses to include boundaries which are not wholly immersed in the noise-generating flow. In particular, it is shown that the pressures exerted on a plane boundary are simply reflections of the quadrupole generators of the flow itself; thus the pressure dipoles account for an enhancement of the quadrupole power, in fact a quadrupling when the wavelength is relatively large, except that degeneration into octupoles occurs for those lateral quadrupoles of the type that would be associated with fluctuations across the shear of an adjacent boundary layer. Under these circumstances it should be possible to estimate the noise of a plane turbulent boundary layer with satisfactory accuracy from sufficient knowledge of the principal quadrupole source strength alone (provided that it is reasonable to neglect the contribution of the fluctuating shear stresses acting on the boundary).
Vibration Isolation of a Rigid Body on Resilient Supports
Authors: Andrews G. J.
Published: September 2005

The equations of motion of a rigid body supported by an arbitrary number of arbitrarily oriented and located resilient mounts with damping are developed with rigor. Their solution is given in a form suitable for high-speed electonic digital computer programing and includes prediction of natural frequencies, static displacements and load distribution to the mounts due to static loading, and frequency response curves for a given isolation system. IBM 704 EDPM and 709 EDPS Fortran computational programs will be supplied on request. An appendix is also included for transforming the inertial properties of a rigid body to a desired frame of reference.
An Experimental Study of the Collapse of a Spherical Cavity in Water
Authors: Mellen Robert H.
Published: September 2005

The pressure wave produced by the collapse of an electrically generated spherical cavity (∼1 cm in radius) in water was measured by means of a small electroacoustic hydrophone (116 in. in diameter) at a distance of 50 cm. The pressure was found to increase as the bubble collapsed according to the t−4/5 (time) law in the interval corresponding to subsonic flow. The pressure then suddenly jumped to a higher value and rapidly decayed to zero. This rapid increase in pressure is assumed to be a shock wave. Using Gilmore's theory for the collapse of the cavity and finite amplitude-wave theory for the pressure wave, we find that the value of the pressure-amplitude characteristic at the shock front corresponds to a cavity-wall velocity approximately equal to the velocity of sound. Since the shock wave has been attenuated, the peak wall velocity must be greater than this value.
Acoustic Relaxation by Radiation
Authors: Lukasik S. J.
Published: September 2005

The effect on the vibrational and rotational relaxation time of de-excitation by photon emission in four gases possessing a permanent electric dipole moment is investigated. Such radiative energy losses are independent of pressure, and may be expected to control the relaxation process at low pressure when collisions become relatively infrequent. Calculations are shown for N2O, OCS, and SO2. Estimates of the efficiency of collisions to deactivate a vibrational level in HCl, indicate that the radiation effect on the vibrational relaxation time of this gas should be the easiest to measure; at a pressure of 10−2–10−3 atmos, de-excitation by radiation should be as important as collisional de-excitation. Radiative de-excitation will become increasingly important at low temperatures because of the consequent increase of the collisional relaxation time.
Ultrasonic Absorption and Velocity in Molten Salts
Authors: Higgs R. W. , Litovitz T. A.
Published: September 2005

Measurements of ultrasonic absorption and velocity were made in the molten salts KNO3, NaNO3, AgNO3, LiNO3, CdCl2, and the molten salt mixture NaNO3-KNO3. The results indicate that these molten salts exhibit a structural viscosity similar to that found in water and associated organic liquids. The ratio of bulk to shear viscosity (ηB/ηS) ran high as 10 in KNO3 and as low as 1.7 in CdCl2. In the Group I nitrates, the ratio ηB/ηS was found to be directly proportional to the volume of the cation. The ln ηB/ηS was found to be a linear function of the entropy of fusion. Consideration of the ultrasonic data in the primary alcohols showed that here also the ln ηB/ηS is a linear function of the entropy of fusion when considering an homologous series. These results indicate that the structural relaxation process in both the ionic and organic liquids involves considerable randomization of the quasi-crystalline liquid lattice.
Velocity and Absorption of Ultrasonic Waves in Several Nonassociated Liquids Under High Pressure
Authors: Mifsud J. F. , Nolle A. W.
Published: September 2005

The ultrasonic-wave velocity and absorption for carbon tetrachloride, benzene, and carbon disulfide are measured by a pulse-reflection method, at several temperatures, in the pressure range of 1 to 1360 atmospheres. Generally similar pressure effects are found in the three liquids. The velocity increases with pressure to about 1.4 times the atmospheric-pressure value, while the relative absorption decreases to about 0.4. The structural relaxation theory, which is examined with reference to carbon tetrachloride, predicts approximately the pressure effect on the absorption at constant temperature, but gives erroneous predictions of the magnitude of the absorption, and of the effects of pressure on the absorption temperature coefficient and on the relaxation frequency. The thermal relaxation theory is partially examined with reference to carbon disulfide, although more extensive data and further refinement of the theory are needed for a rigorous test. In terms of this theory, the absorption data are consistent with approximate theoretical predictions of the effect of pressure upon the relaxation frequency and upon the relaxational portion of the specific heat. Over all, the study tends to confirm the thermal relaxation theory of the excess absorption in nonassociated liquids. It is shown also that the Tonks equation of state gives approximately correct values of the pressure coefficient of sound velocity for carbon disulfide.
Stress and Strain Limits on the Attainable Velocity in Mechanical Vibration
Authors: Hunt F. V.
Published: September 2005

The maximum peak velocity which can be developed at the free end of a slender rod driven at resonance in a normal mode of longitudinal vibration is given by v0 = c0Sxx, where c0 is the Young's-modulus speed of sound (E/ρ)12 and Sxx is the limiting value of extensional strain for the rod material. The ratio of allowable stress to the maximum peak velocity is given by Txx/v0 = ρc0, where the characteristic specific impedance plays in this case the role of a transfer impedance relating the stress at a node to the velocity at an antinode. The same expressions describe, within half an order of magnitude, the relations between the maximum allowable stress or strain and the normal component of velocity at the antinodes of displacement for thin uniform bars or plates and for wedges or cones vibrating in flexure, and for an exponential solid horn vibrating longitudinally. By inductive extension it is argued that within the indicated precision the same velocity-strain ratios prevail in the vibration of any elastic body however excited.
Propagation of Longitudinal Waves and Shear Waves in Cylindrical Rods at High Frequencies
Authors: McSkimin H. J.
Published: September 2005

Exact steady-state solutions for both longitudinal waves and shear waves traveling in isotropic rods of circular cross section are analyzed. Numerical examples are described for rods of large diameter to wavelength ratio.

The effect of mode conversion on the propagation of short duration longitudinal wave trains is considered; and an approximate expression for the resulting loss is developed.

Experimental results for 10–25 Mc/sec longitudinal and shear waves in fused silica rods of 1.13 cm radius are described.
Dynamics of the Vibration Sense at Low Frequency
Authors: Eijkman E. , Vendrik A. J. H.
Published: September 2005

The dynamic properties of the vibration sense in the human skin were investigated by means of psycho-physical methods using stimuli with different time courses. Sinusoidal deformations and deformations linearly increasing with time were used. Up to frequencies of 30 cps the results are described very well by a differentiating system having a time constant of about 30 msec. This is in good agreement with electrophysiological observations. Also in agreement with electrophysiological experiments, “rectifying” properties are found. Possible mechanisms underlying these phenomena are discussed.
Diffraction of a Longitudinal Pulse from a Wedge in a Solid
Authors: Grannemann W. W.
Published: September 2005

The diffraction theory developed by Sommerfeld and extended by Pauli is used to approximate the relative amplitude of the diffracted pulses from a wedge in a solid. The geometric terms are neglected and the amplitude of the diffracted wave is obtained from the contour integral. Barium titanate transducers are used for sources and receivers on tar and concentrate models to check the predictions of the theory. Several relative amplitude versus distance curves are given for regions where the diffracted pulse is separated from other waves. The experimental and theoretical curves agree to ±4 decibels in the regions tested.
Theory of Signal Detectability as an Interpretive Tool for Psychophysical Data
Authors: Tanner Wilson P.
Published: September 2005

The theory of signal detectability is examined from the standpoint of determining a set of satisfactory assumptions for the purpose of developing an interpretive tool for use in psycho-physical experiments. It is concluded that the assumption that the observer attempts to maximize the expected value of the outcome of the experiment is satisfactory for this purpose, and that a set of physical conditions can be established which justify a computation of the detectability of a signal in noise based on a finite sampling plan involving 2WT amplitude values over the open interval, 0 to T.
Frequency Measure of the EEG
Authors: Norkus F. J. , Derbyshire A. J. , Mills P. J. , Carter R. L.
Published: September 2005

The use of electroencephalograms for the evaluation of auditory function has proven to be invaluable, especially where the standard audiogram is not possible. In sleeping subjects there is a definable change in the EEG pattern upon the presentation of an auditory stimulus. One method of analysis of the brain's response to a tone is the measurement of shifts in frequency of the brain wave, recorded simultaneously with the electroencephalogram. This recording of frequency changes is later analyzed for indications of reception of the tones presented. An electronic frequency recorder which is used in conjunction with a standard polygraph is described. The cortex has indicated response when the recorder produces a shift in frequency. This shift occurs within a specified time interval after the presentation of tone (the “delay time” of the response).
Experimental Study of the Relative Intelligibility of Alphabet Letters
Authors: Curry E. Thayer , Fay Thomas H. , Hutton Charles L.
Published: September 2005

This preliminary study was designed to ascertain the relative intelligibility of the twenty-six individual spoken alphabet letters when presented to normal listeners over a 45-db range of levels. The gain function for the pooled results of 26 letters spoken by three experienced speakers to 18 listeners has a sigmoidal shape. The 15-db increase in presentation level from 10 to 25 db yields a 65% increase in correct identification for all letters. The average slope of the pooled curve for all letters between 20 and 80% was 4.34% per db. The curves appear to be similar to those of the more difficult stimuli such as the monosyllable PB lists and unselected disyllabic lists. Percentages of correct identifications for each letter at each presentation level are also presented.
Working Model Illustrating the Cross Section of the Cochlea Mechanically
Authors: Meyer Max F.
Published: September 2005

This model serves a totally different purpose from that which shows through transparent windows what goes on lengthwise in the cochlea. [M. F. Meyer, Am. J. Psychol. 72, 293–296 (1959). The former model is still working and is now in the possession of Professor James P. Egan of Indiana University.] The presently described model shows what hypothetically happens crosswise. It is made of dry ties of several materials, not of tubing filled with a liquid.
Effect of Dissolved Air on the Speed of Sound in Water
Authors: Greenspan Martin , Tschiegg Carroll E.
Published: September 2005

A sing-around ultrasonic velocimeter was used to show that dissolved air has a negligible effect (less than 10 ppm) on the speed of sound in water at 31.8°C and 0°C.
Energy Flux from an Acoustic Source Contained in a Moving Fluid Element and Its Relation to Jet Noise
Authors: Ribner H. S.
Published: September 2005

It is found that a high-frequency source (or multiple) imbedded in a moving patch of fluid emits a constant acoustic power independent of the motion. (The directivity is, however, altered). This holds when the wavelength λ ≪ radius R′ of the entire region of flow. At the other extreme λ ≫ 2πR′ it appears that the acoustic power is enhanced by the motion, somewhat (but not exactly) as the emission of a source is enhanced by motion through fluid at rest. A typical wavelength of a radiating eddy in a jet lies between the two extremes and a limited convective enhancement of the power is inferred. The amount should be less than that predicted by Light-bill or the much more conservative values suggested by the work of Ribner; it could conceivably lie within experimental error. justifying the nonconvective law, power ∼U8, found by measurement.
Underwater Sound Absorbing Structures
Authors: Cramer W. S. , Johnston T. F.
Published: September 2005

Some historical background on the use of metal-loaded robbers for acoustical purposes is presented. Data are given which show that the performance of sound absorbing wedges is improved by adding air-filled cylindrical holes.
Calorimetric Measurement of Ultrasonically Produced Strains in Solids
Authors: West Forrest G. , Einspruch Norman G.
Published: September 2005

An experiment for the calorimetric determination of the strain produced in a solid material at low temperature by a megacycle frequency ultrasonic wave is proposed. A calculation is presented in order to demonstrate that if the strain amplitude is of a magnitude frequently estimated, it should be readily measurable.
Growing Points in Multichannel Communication
Authors: Broadbent D. E.
Published: September 2005

The numerous experiments on multichannel listening allow certain broad conclusions: that the listener has a limited capacity, that therefore much of the information presented to him is discarded, and that this discarding is made easier when the signals to be ignored share certain physical characteristics which the desired signals do not have. These conclusions suggest further lines of advance. The same speech signals may interfere with each other more when they are chosen from a larger ensemble. This implies that the information content must be considered. In addition, momentary peaks of information are handled by a curious form of immediate memory in the listener.
On the Transmission and Confirmation of Messages in Noise
Authors: Egan James P. , Clarke Frank R. , Carterette Edward C.
Published: September 2005

In several experiments, the restrictions imposed upon the communication process by an articulation test were relaxed by increasing the number of events in the communication sequence. A communication event is the transmission of a message from the source to the receiver followed by the return of a message (correct or incorrect) from receiver to source for confirmation. Although both source and receiver serve as talker and listener, the relation between them is asymmetric. Since the source knows the original message, he must accept or reject the message sent back to him according to some criterion.

Various types of communication events arise depending upon (1) whether or not the receiver correctly hears the message, and (2) whether or not the source confirms the message returned by the receiver. The various probabilities associated with these events are investigated as a function of speech-to-noise ratio. The behavior of the source is examined in terms of the relation between the two conditional probabilities associated with a correct and with an incorrect confirmation.

If each message is sent repeatedly until all are confirmed, a sequence of communication events is generated. A simple mathematical model accurately describes this process.
Diffraction of an Elastic Pulse in a Loaded Half-Space
Authors: Fredricks R. W.
Published: September 2005

The problem of the diffraction of a plane compression pulse by a rigid, incompressible semi-infinite body in lubricated contact with a homogeneous, isotropic, perfectly elastic half-space is formulated by a potential function and separation of variables approach. The boundary conditions are expressed by dual integral equations that are solved by a function-theoretic technique. The exact solution is obtained, as a function of space and time variables, in a closed form.
Automatic Processing System for Acoustical Data
Authors: Parker Winston E. , East Larry Y.
Published: September 2005

An improved instrumentation system has been developed to analyze the dynamic pressure field produced by jet aircraft. The system is automatic and utilizes analog computer techniques to obtain an accuracy of ±0.2 db in its readout. The method used is to secure a true rms value of octave band segments of the jet noise spectrum and to convert this to decibels by the use of a dc logarithmic amplifier. The transition to acoustical decibels is made by obtaining the difference between this voltage and another voltage obtained from a reference oscillator. The value of this reference oscillator in acoustical decibels is obtained by comparing its output voltage to that of a calibrated microphone. The dynamic range of the system has proved more than adequate for greater than 98% of the data processed by this unit during the time this system has been in operation. The output is in the form of punched cards for utilization with a digital computer.
Studies of Formant Transitions Using a Vocal Tract Analog
Authors: Stevens Kenneth N. , House Arthur S.
Published: September 2005

An electrical analog of the vocal tract is used to obtain experimental relations between certain idealized articulatory parameters and formant frequencies associated with the transitional and stop portions of vowel-consonant syllables. The data are discussed in terms of the “locus hypothesis” proposed by Delattre, Liberman, and Cooper [J. Acoust. Soc. Am. 21, 769 (1955)] and in terms of simple resonator theory. It is concluded that the results modify the hypothesis that assigns one second-formant locus to all vowel-consonant transitions involving a given class of stop consonants. In particular, the second-formant loci for transitions to velar and bilabial stop consonants appear to vary over a range of frequencies depending on the vowel, while loci for post-dental stop consonants are relatively invariant. Characteristics of first- and third-formant loci are discussed briefly.
Base Pressure Fluctuations
Authors: Eldred Kenneth McK.
Published: September 2005

The intense vibration accompanying the extension of dive brakes and other high-drag devices on aircraft and missiles has been observed for many years. Recently, considerable vibration has been experienced at the fundamental longitudinal mode and at other internal resonance frequencies of a vehicle which had a blunt base during the maximum dynamic pressure phase of flight. In both cases the vibration is believed to result from the turbulent fluctuations in the wake of the base or drag device.

The base pressure fluctuations have been measured at two base positions on a small body of revolution at eleven points in the velocity range of 68 to 352 ft/sec. The results show that: (a) The ratio of (〈p2〉nv/q2)12 varies between 0.007 at the center of the base to 0.015 at 65% radius; (b) The spectrum of the pressure fluctuations is a function of the body Strouhal number; (c) The variation of observed vibration response with flight parameters can be predicted from the base pressure fluctuation data.
Naturalness and Distortion in Speech-Processing Devices
Authors: David E. E.
Published: September 2005

In evaluating a speech-processing device, the result of applying a suitable fidelity criterion to its output and the tolerance within which the reduced signals must be represented to satisfy this criterion, as well as the corresponding band width, are important. These factors establish a measure of the efficiency of the particular representation achieved by the device. This quantity can be utilized to compare it with systems having known characteristics. An important constraint is that the systems being compared have equal fidelity according to the criterion being used. The quantitative result of this comparison depends markedly upon the criterion selected. It should be chosen with the contemplated application in mind and can be either objective or subjective in nature. Since speech-processing devices operate on the basis of an objective criterion, it appears that as future research establishes relations between subjective impressions and physical measurements, better and perhaps even the ultimate speech-processing devices will become realities.
Comparison of Directly Measured Sound Velocities with Values Calculated from Hydrographic Data
Authors: Hays Earl E.
Published: September 2005

Hydrographic data (temperature, salinity, depth) and directly measured sound velocities were obtained from a section made at 6°E across the Mediterranean Sea in June and July, 1959. Sound velocities were calculated from the hydrographic data and compared with the measured values. Two methods were used to calculate the sound velocity from the hydrographic data. One method used Del Grosso's zero depth values with the depth correction from Matthew's tables. (This has been the usual method of calculation at the Woods Hole Oceanographic Institution until now.) The other method used the empirical equation of Wilson derived from laboratory measurements made at the Naval Ordnance Laboratory. The significant difference observed in the comparisons appears below 200 m. Here the corrections using Matthew's tables result in too large values for the velocities at depth, the magnitude of the difference being about 2.5 m/sec at 2500 m depth. The calculated values from Wilson's equation agree with the experimental values more closely (about 0.5 m/sec difference at 2200 m depth).