摘要:

Measurements of the attenuations of face‐centered metals by Bordoni have shown attenuation peaks at low temperatures. By using the measurements of Bömmel on single crystal lead it can be verified that this is a relaxation and values can be obtained for activation energies and frequency terms. It is shown that the measured results correlate well with a relaxation due to the displacement of a dislocation from one atomic line to an adjacent one against the limiting shearing stress of the crystal. The limiting shearing stress measured for four face‐centered metals is in good agreement with theoretical calculations of Cottrell.A higher temperature loss is also measured which increases exponentially with the temperature. It is shown that this term is due to breakaway of the dislocation from its impurity pinning points due to thermal agitation. This breakaway abstracts energy from the vibration and produces a loss independent of the frequency but increasing with temperature since more breakaways occur at higher temperatures. The activation energy of breakaways correlates well with the binding energy of impurity atoms.

ISSN:0001-4966    

DOI:10.1121/1.1907985

出版商:Acoustical Society of America    

年代:1955

数据来源: AIP

摘要:

Quantitative measurements have been performed on some fundamental phenomena caused by ultrasonic cavitation, i.e., the synthesis of hydrogen peroxide, the oxidation of potassium iodide, the decomposition of carbon tetrachloride, the degassing action, and the evolution of heat in connection with the cavitation process. The experiments were made under controlled and defined acoustic conditions (standing waves, progressive waves, and non‐resonance) and the influences by various important factors (acoustic intensity, gas content) have been evaluated.Tentative theories of the cavitation process and allied phenomena are evaluated on the basis of the experimental results. Cavitation chemistry is found to be similar to gamma radiation chemistry (pH‐dependence of the yield of hydrogen peroxide, oxidation of solutes, necessity of oxygen). Cavitation is assumed to be preceded by a homogeneous nucleation process in which a germ or gas nucleus is being formed by rupture of the liquid around this germ. Ionization of some of the gas molecules entrained in the cavity will take place in order to establish the electric charge of the surface of the cavity. Two hydrogen peroxide molecules are formed for every ionized oxygen molecule. It is supposed that in the case of oxygen a cluster is formed by the combination of two water molecules and a positive oxygen ion. This cluster yields on decomposition at the neutralization two hydroxyl radicals and one excited hydrogen perioxide molecule.The rate of cavitation seems to be independent of (1) the gas concentration (above the threshold concentration), (2) the pressure amplitude (above the threshold amplitude and within the region of cavitation), and (3) the nature of the dissolved gas (provided the gas may initiate homogeneous cavitation at all). These features indicate that properties of the liquid are rate determining when the various threshold requirements are fulfilled. A tentative picture of the nucleation process is presented, which seems to satisfy these conditions.The degassing action in an ultrasonic field proceeds to half saturation practically independent of the intensity.A method for cavitation dosimetry is described.

ISSN:0001-4966    

DOI:10.1121/1.1907987

出版商:Acoustical Society of America    

年代:1955

数据来源: AIP

摘要:

In the described instrument ten‐microsecond, 30‐Mc carrier pulses reflected from a resonant layer allow a theoretical precision of 0.1 percent in making velocity determinations while using less than 0.1 cc of test liquid. By the same technique, ultrasonic absorption can be measured in highly dissipative liquids using layers about 0.1 mm thick. Water velocities observed at 30 Mc are presented along with values by others in the range of 0° to 93°C.V = 1554−0.0305(68.4−T)2is proposed as the best empirical parabola to accommodate the available data, and an additional cubic correction formula is suggested.

ISSN:0001-4966    

DOI:10.1121/1.1907989

出版商:Acoustical Society of America    

年代:1955

数据来源: AIP

摘要:

Measurements have been made of the ultrasonic velocities in polarized barium titanate ceramic blocks for both compressional and transverse waves, parallel and perpendicular to the axis of polarization. Some variation in compressional velocity with the degree of binding was evident. The largest variation between the velocities for transverse waves causing shear amounted to nearly 12 percent and proved to be accounted for by electromechanical coupling. The compressional velocity parallel to the axis of polarization ran some four percent higher than that at right angles. Here again it appeared that the effect was caused principally by differences in electrical boundary conditions and that the constant field elastic constants varied only slightly with polarization.

ISSN:0001-4966    

DOI:10.1121/1.1907991

出版商:Acoustical Society of America    

年代:1955

数据来源: AIP

摘要:

Acoustical velocities were measured at 500 kc in a number of organic liquids and binary solutions prepared therefrom. A precision ultrasonic interferometer was employed. For the most part sound velocities were found to vary linearly with temperature. Densities were determined at 20°C. Adiabatic compressibilities at 20°C were calculated and some conclusions drawn concerning the cohesive properties of certain of the solutions. The molecular sound velocity in a binary liquid solution is the sum of the products of the respective molecular sound velocities in the pure liquids by their corresponding mole fractions all at the same temperature. Where practicable, effective molecular radii were calculated from the data. The usefulness of the molecular weight of a liquid in predicting values of the temperature coefficient of velocity is discussed. Apparently many more experimental data are needed before an adequate theoretical analysis is possible.

ISSN:0001-4966    

DOI:10.1121/1.1907993

出版商:Acoustical Society of America    

年代:1955

数据来源: AIP

摘要:

The attenuation of normal modes in a two‐layered fluid medium due to absorption in the lower semi‐infinite layer is calculated under the assumption that this absorption is small. The result obtained gives the attenuation coefficient for each mode as the product of the absorption coefficient for plane waves in the absorbing layer and a dimensionless function of wavelength and layer depth. Curves of this dimensionless function are plotted for the first five modes in cases typical of propagation in shallow water over a sand and a mud bottom. The results indicate a very rapid decrease in attenuation as the frequency rises above the cut‐off frequency, where it is just equal to the bottom absorption. At higher frequencies the attenuation varies as (n2λ3/H3)α, wherenis the mode number, λ the wavelength,Hthe water depth, and α the absorption coefficient in the bottom (α may itself be a function of frequency). The latter result is also derived by a less rigorous method.

ISSN:0001-4966    

DOI:10.1121/1.1907995

出版商:Acoustical Society of America    

年代:1955

数据来源: AIP

摘要:

An anechoic lining for underwater sound use can be made from waterproofed, rubberized, horsehair batting. It decreases the reflectivity 20 db below that obtained from a steel wall over a frequency range from 100 kc to 400 kc and for a wide range of angles of incidence. It is inexpensive, easily installed, and can be used for several 8‐hour periods before additional waterproofing is necessary.

ISSN:0001-4966    

DOI:10.1121/1.1907997

出版商:Acoustical Society of America    

年代:1955

数据来源: AIP

摘要:

The acoustical radiation scattered from a sinusoidal surface of zero pressure insonified by an obliquely incident plane wave of sound is obtained as an infinite series of waves whose coefficients may be determined by means of a recurrence relation. The corresponding analysis is presented for the case of a spherical source of radiation. At points sufficiently remote from the surface only a finite number of terms need be included. Each coefficient in the series is itself an infinite series which converges most rapidly when the height of the surface corrugations is small compared to the wavelength of the incident sound. Application is made to determine the average intensity and fluctuation of the sound reflected from a travelling sinusoidal boundary. The degree of roughness required to destroy the effect of Lloyd mirror fringes is discussed in terms of the ratio of the surface height and wavelength to the wavelength of the incident sound.

ISSN:0001-4966    

DOI:10.1121/1.1907999

出版商:Acoustical Society of America    

年代:1955

数据来源: AIP

摘要:

A general expression for the radiation impedance of theqth source in an array ofnsources has been obtained in terms of Green's functions. It is applicable to finite sources or to sources which are mounted in finite baffles provided the Green's function can be found. The theory is applied to an array of finite cylinders which form part of an infinitely long rigid cylindrical baffle. Ifka≪1, the radiation resistance of each member can easily be expressed in terms of sine integrals. Curves showing the radiation resistance of each member of an array of five cylinders are given. The effect of varying the separation is also shown.

ISSN:0001-4966    

DOI:10.1121/1.1908001

出版商:Acoustical Society of America    

年代:1955

数据来源: AIP

摘要:

The impedance presented to the inside surface of a hollow, radially vibrating, liquid‐filled cylinder of lengthlwhich is mounted in the aperture of a rigid wall of thicknesslhas been determined. It was assumed that radiation from the ends of the cylinder into the infinite liquid media (water) takes place symmetrically with respect to the plane midway between the ends of the cylinder. The liquid within the cylinder need not be the same as the liquid outside the cylinder. Although the impedance at any frequency can be obtained from the results, an approximation is introduced which is valid when the wavelength in the liquid within the cylinder is such thatka⩽π/2 (kbeing the wavelength constant andathe inside radius of the cylinder). Under these circumstances it is found that the output power drops to zero whenever the length of the cylinder equalsnλ, wherenis an integer and λ is the wavelength of sound in the contained liquid.

ISSN:0001-4966    

DOI:10.1121/1.1908003

出版商:Acoustical Society of America    

年代:1955

数据来源: AIP