Browsing by Author "Johnson, Earl Mead"
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Item Second sound in counter flowing superfluid and normal fluid(1968) Johnson, Earl Mead; Hildebrandt, A. F.; Collins, R. Eugene; Waller, R. H.From ordinary hydrodynamics it is known that an "entrainment" of sound occurs in a moving fluid. A similar effect is expected to take place in the hydrodynamics of helium II. A measurement has been made of the change in time of flight of a second sound pulse as a function of the relative velocity (v[lowered n] - v[lowered s]), where v[lowered n] is the normal fluid velocity and v[lowered s] is the superfluid velocity. From this measurement we may infer how the reference frame of second sound varies with the motion of the normal fluid and superfluid. The change in time of flight was measured within ±0.14 x lO[raised -6] seconds.Item Second sound in counterflowing normal and superfluid Helium II(1971) Johnson, Earl MeadFrom ordinary hydrodynamics it is known that an "entrainment" of sound occurs in a moving fluid. A similar effect is expected to take place in the hydrodynamics of Helium II. A measurement has been made of the change in the time of flight of a second sound pulse as a function of the relative velocity (v[lowered n] - v[lowered s]), where v[lowered n] is the normal fluid velocity and v[lowered s] is the superfluid velocity. A temperature range of 2.10°K through 1.00°K was covered. A typical time of flight at 1.75°K for a second sound pulse for stationary conditions was 5.8622 milliseconds. The change in the time of flight for a normal fluid velocity of 0.4 cm/sec at 1.75°K was 0.7 microseconds. Each time of flight for the second sound pulses was measured within [plus-minus] 0.1 microseconds.