摘要:

It is proposed that acoustic nuclear magnetic resonance be used to detect steady‐state nuclear orientation achieved by the Jeffries Abragam effect. This is a new scheme for double magnetic resonance (ADMR) in contrast with conventional DMR, which employs the usual time‐varying magnetic field to observe the enhancement of the nuclear resonance. The acoustic wave modulates the nuclear quadrupole interaction to induce double as well as single spin flips. Calculations for nuclei of spinI = 32in weak dipolar coupling with paramagnetic electrons of spinS = 12in an axial crystal indicate that both types of DMR should give positive and negative enhancements ∼gβ /gnβn∼103for 1° ⩽T⩽ 300°K in favorable circumstances. Suitable samples in which the effect might be demonstrated are iodine nuclei in NaI containingI2−centers and27Alnuclei inCr3+orV3+dopedAl2O3. If the related experiments are performed, the effect of the electron paramagnetic resonance linewidth and of nuclear‐spin diffusion may well reduce the enhancement by one or two orders of magnitude.

ISSN:0001-4966    

DOI:10.1121/1.1910379

出版商:Acoustical Society of America    

年代:1967

数据来源: AIP

摘要:

New measurements of the velocity of sound in water over a wide range of temperatures and pressures have been made and are used to calculate the nonlinearity parameterB/Ain the temperature range from 0° to 80°C and at pressures to about 10 000 kg/cm2. It is found that, for low temperatures,B/Arises to a broad maximum at about 3000 kg/cm2and then slowly decreases. At the highest temperatures,B/Adecreases very slowly with increasing pressure. At 1 atm pressure, theB/Avalue for 0°C is the lowest calculated at any temperature and pressure, andB/A increasesmonotonically with temperature in the range covered. However, at 3000 kg/cm2, theB/Avalue for 0°C is the largest obtained, andB/A decreaseswith increasing temperature. The values ofB/Arange from a low value of 4.08 at 1 atm and 0°C to 6.80 at 3000 kg/cm2and 0°C.B/Ais found to be relatively insensitive to temperature and pressure. The usefulness ofB/Ameasurements as a means of studying the liquid state is discussed.

ISSN:0001-4966    

DOI:10.1121/1.1910380

出版商:Acoustical Society of America    

年代:1967

数据来源: AIP

摘要:

The variation of the relative intensity of cavitation with temperature has been determined by chemical and erosion methods. The endeavor was to employ both methods under identical conditions of transducer frequency, power input to the transducer, height of test samples over the transducer face, etc. The liberation of chlorine from a saturated solution of carbon tetrachloride in water withortho‐tolidine reagent as indicator was employed in the chemical method and cavitation intensity was expressed as the optical density of the resulting yellow solution for blue light of 436 mμ. An expression of optical density in terms of peak percentage absorption of the yellow solution was used to stress observations in this method of determining cavitation activity. In the erosion method, lead samples were used and the intensity of cavitation was expressed as the loss in weight of the sample after exposure to cavitation. The results obtained were fed into a computer and equations derived for the respective measurements. These results and other observations on the experimental work are discussed.

ISSN:0001-4966    

DOI:10.1121/1.1910381

出版商:Acoustical Society of America    

年代:1967

数据来源: AIP

摘要:

In order to investigate the effect of solid impurities on cavitation, the distribution functions of nuclei were studied in water samples that had various impurities and were differently treated: filtered, placed under a lead screen, de‐ionized, or with addition of uranyl nitrate. We have used two kinds of impurities : wettable particles (emery and corundum) and unwettable particles (Teflon). Although the results give support to Harvey's stabilization theory, the action of impurities is not simply a stabilizing one; the impurities play an active role in determining the shape of the distribution functions. The unwettable impurities cause a production of large‐size nuclei, while the wettable ones destroy large nuclei and increase the concentration of small nuclei. A phenomenological treatment of the mentioned effect is suggested.

ISSN:0001-4966    

DOI:10.1121/1.1910382

出版商:Acoustical Society of America    

年代:1967

数据来源: AIP

摘要:

The magnetic‐field variation of the attenuation of 8.5‐, 24‐, and 56‐Mc/sec sound waves propagating in liquid gallium was measured in fields up to 146 kG. The attenuation was found to increase monotonically with field and is in good agreement with the predictions of Anderson's theory.

ISSN:0001-4966    

DOI:10.1121/1.1910383

出版商:Acoustical Society of America    

年代:1967

数据来源: AIP

摘要:

A system is discussed for the instrumentation of infrasonic and hydromagnetic waves traveling through the atmosphere and the ionosphere. Two large missiles were used as the sources of energy. The advantages of the instrumentation system are: a minimum of manpower and time is required to calibrate and place the system into operation; the system is easily transported; and the system is very stable over long periods of time. A description of the missile engines as a moving source of energy in the infrasonic‐frequency spectrum (20–0.025 cps) was obtained. It is concluded that the instrumentation system has the capability of providing reliable data on long period waves and that the equipment is stable.

ISSN:0001-4966    

DOI:10.1121/1.1910384

出版商:Acoustical Society of America    

年代:1967

数据来源: AIP

摘要:

Experimental and theoretical attenuation characteristics are presented for broadband and pure tone acoustical signals between 300–1200 cps traveling through long pipes with rigid walls. Close correlation was found between experimental and theoretical attenuation rates over the entire system; however, an unexpected, almost constant attenuation factor was found in 90° side branches. The experimental work was sponsored by the American Gas Association as part of a sonic‐leak pinpointing project.

ISSN:0001-4966    

DOI:10.1121/1.1910385

出版商:Acoustical Society of America    

年代:1967

数据来源: AIP

摘要:

The propagation of infrasonic waves in a realistic model atmosphere which includes a variable wind profile as well as a variable temperature profile is discussed quantitatively for wave periods between 1–10 min. The numerical method used for the computation of phase and group velocity curves and other characteristic quantities associated with the possible guided modes is an extension of the multilayer method used previously by Press and Harkrider and by Pfeffer and Zarichny for atmospheres without winds. The effects of winds on the propagation are assessed by examining computations carried out for various fixed directions of the horizontal group velocity and from the computation of deviations of the phase‐velocity direction from group‐velocity direction for the case of propagation crosswind. Pressure height profiles of various frequencies propagating in various modes are exhibited and excitation amplitudes for ground level sources (excluding the frequency spectrum of the source) are plotted versus frequency for various modes and various group‐velocity directions. Qualitative explanations of the computed results are given, and the implications of the results to actual waveforms are discussed.

ISSN:0001-4966    

DOI:10.1121/1.1910386

出版商:Acoustical Society of America    

年代:1967

数据来源: AIP

摘要:

Tensorial equations of motion are considered in order to attack the problem of the separation of the stress equations of motion in nonhomogeneous isotropic elastic media. We confine ourselves to the plane equations in a medium whose elastic coefficients and density are arbitrary functions of a single Cartesian coordinate. It is shown that the stresses are expressible in terms of a single function satisfying a fourth‐order ordinary differential equation. The solution obtained may be useful in studying surface waves in nonhomogeneous media.

ISSN:0001-4966    

DOI:10.1121/1.1910387

出版商:Acoustical Society of America    

年代:1967

数据来源: AIP

摘要:

An appropriate Green's function is used to obtain simple sounds on the average energies of randomly excited, nonuniform linear beams.

ISSN:0001-4966    

DOI:10.1121/1.1910388

出版商:Acoustical Society of America    

年代:1967

数据来源: AIP