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Reported instances of stable nonflow in He II Josephson effect experiments have in most cases been achieved by a flow of liquid helium from one reservoir to another, a flow driven by ultrasonic pumping. We have examined some of the characteristics of this pumping. We confirm that a threshold transducer power is necessary to initiate pumping and find that the threshold power has a temperature dependence of ρsTα, 0 < α < 1, in the range 1.5 K < T < 2.1 K. A capacitor has always been used by others to measure the meniscus level. We find that the geometry of the core of this capacitor is important: when the core bottom is conical, with vertex pointing down, we achieve no pumping. We find that the orientation of an asymmetric pinhole plays no role. Finally, the pumping speed is a monotonic function of transducer power for powers exceeding threshold and for powers less than an upper limit, above which there is no further increase in pumping speed. [ABSTRACT FROM AUTHOR]

Most aspects of acoustic streaming were considered understood in 1954. The time dependence of its onset, however, was controversial when Liebermann's measurements, valid for slowly developing streaming, were criticized. The criticism cited a report that streaming was present only 20 msec after turning on the acoustic source. Using a thermistor bead as flow meter, we have observed the time dependence of the onset of streaming in two fluids of widely different viscosity, each in two vessels of different geometry. The time dependence of the streaming velocity is described as follows: There is zero time derivative at the start. This is followed in succession by a positive second derivative, inflection point, and negative second derivative which persists during an approach to a steady state flow. From the start to the inflection point, the flow velocity v depends on time t according to v = btp where b and p are empirical constants. The exponent p appears to be a nearly fundamental property of streaming onset while b is sensitive to the experimental circumstances. Important to the controversy is that the development is safely slow enough to validate Liebermann's measurement technique, typically taking two seconds to reach the inflection point and five seconds to reach 90%. of steady flow. [ABSTRACT FROM AUTHOR]

A group of hydrophone elements uniformly and closely spaced along a straight line is used to measure the angle of arrival of sound waves. By sampling the outputs of these elements rapidly and in succession, one simulates single hydrophone moving relative to the sound waves. The signal measured at the output has a frequency given by the Doppler equation f=f0(1 +α cosθ), where f0 is the frequency of the sound in the water, α is the ratio of the scanning speed to the speed of sound, and θ is the bearing angle desired. The theoretical results expected along with the experimental measurements which confirm the theory and a description of the equipment used are included. It was found that the scanned system simulates almost exactly a single moving point hydrophone, and the Doppler equation was found to hold. Pure tones and narrow-band noise signals are shifted in frequency. The angular resolution was found to be equal to the ratio of the wavelength of the sound to the component of the hydrophone length normal to the direction of sound propagation. [ABSTRACT FROM AUTHOR]

An attempt is being made to employ independent hydrophone elements uniformly spaced along a straight line to deduce the bearing of an incoming plane sound wave. Upon sampling the outputs of the hydrophone elements in succession, one simulates a single hydrophone moving relative to the sound wave. The signal measured in such a case would have a frequency of f=f0 (1 - α cosθ) where f0 is the frequency of the sound, α is the ratio of the scanning speed to the sound speed, and θ is the bearing angle to be deduced from a measurement of f. A method to accomplish this was outlined in a paper presented at the June, 1960 meeting of the Society. Since then a hydrophone about four feet long containing 134 independent elements has been obtained and the necessary switching and sampling circuits built to test the method experimentally. Measurements made in a laboratory tank confirm the theoretical results very nicely for a steady signal. These together with the results obtained using a pulsed signal and the effects of noise on the system will also be presented. [ABSTRACT FROM AUTHOR]

An attempt is being made to employ independent hydrophone elements uniformly spaced along a straight line to deduce the bearing of an incoming plane sound wave. Upon sampling the outputs of the hydrophone elements in succession, one simulates a single hydrophone moving relative to the sound wave. The signal measured in such a case would have a frequency of f = f0 (1 - α cos θ) where f0 is the frequency of the sound, α is the ratio of the scanning speed to the sound speed. and θ is the bearing angle to be deduced from a measurement of f. If two mutually orthogonal lines of hydrophones are used in the horizontal plane, the azimuth of the incoming sound wave can be determined uniquely, and the elevation angle can be found with 'up vs down' ambiguity present. Calculations show that the limit of solid angle resolution is determined by the ratio of the wavelength to hydrophone array length. The solid angle resolution is calculated from the bearing resolution Δθ = π N for a single line hydrophone where N is a number > 1. The necessary minimum number of hydrophones per unit length depends upon the arbitrary choice of α and the Shannon Sampling Theorem. The signal-to-noise ratio improves with increasing resolution, the improvement being proportional to N. [ABSTRACT FROM AUTHOR]

A systematic determination of the electromechanical coupling coefficient k has been made for Fe-Al alloys containing aluminum percentages between 12 and 14 by weight and annealed at temperatures between 600°C and 1100°C. For annealing temperatures in the neighborhood of 1000°C, k2 is about equal to 0.05 and is nearly independent of composition, a result in agreement with earlier measurements of Masumoto. For lower annealing temperatures, k2 becomes sensitive to composition, the highest value measured being equal to 0.12 for an alloy containing 12.3% Al and annealed at 650°C. In all cases eddy current losses are lower for Fe-Al than for soft annealed 'A' nickel. [ABSTRACT FROM AUTHOR]