The emission of sound by statistically homogeneous bubble layers

This paper is concerned with the flow of a bubbly fluid along a wavy wall, which is one Fourier component of a linearized hydrofoil. The bubbles are dispersed, not throughout the whole of the liquid, but only over a certain distance from the wall, as occurs in practice with cavitation bubbles. Outside the bubbly regime there is pure liquid. The interface between the bubbly fluid and pure liquid fluctuates for various reasons. One of these is the relative motion between bubbles and liquid. This is considered here in detail. A calculation is made of the sound emitted by the bubbly layer into pure liquid as a result of this stochastic motion of the interface

Magnetic flux density and the critical field in the intermediate state of type-I superconductors

To address unsolved fundamental problems of the intermediate state (IS), the equilibrium magnetic flux structure and the critical field in a high purity type-I superconductor (indium film) are investigated using magneto-optical imaging with a 3D vector magnet and electrical transport measurements. The least expected observation is that the critical field in the IS can be as small as nearly 40% of the thermodynamic critical field $H_c$. This indicates that the flux density in the \textit{bulk} of normal domains can be \textit{considerably} less than $H_c$, in apparent contradiction with the long established paradigm, stating that the normal phase is unstable below $H_c$. Here we present a novel theoretical model consistently describing this and \textit{all} other properties of the IS. Moreover, our model, based the rigorous thermodynamic treatment of observed laminar flux structure in a tilted field, allows for a \textit{quantitative} determination of the domain-wall parameter and the coherence length, and provides new insight into the properties of all superconductors.Comment: 5 pages, 5 figure

Measurement of the n=2 Lamb shift in He+ by the anisotropy method

A high-precision measurement of the 2s 2S1/22p 2P1/2 Lamb shift in He+ by the quenching-anisotropy method is reported. The theory and experimental method are described in detail. The measured value of 14042.520.16 MHz (11 parts per million) rivals the accuracy of Lamb-shift measurements in hydrogen by microwave resonance. By subtracting the known low-order terms in the Lamb shift, we interpret the results as a measurement of the order (Z)6mc2 and higher contributions to the electron self-energy GSE(Z). The various contributions to the Lamb shift are discussed, and a revised value for GSE(Z) at low Z is extracted from high-Z calculations. The theoretical value for the Lamb shift is 14042.510.2 MHz, in excellent agreement with experiment. The results provide the most sensitive available determination of GSE(Z) for low Z. Measurements and calculations for hydrogen and other members of the isoelectronic sequence are discussed. © 1991 The American Physical Society

Asymmetry measurement of the 2s1/2(hy1s1/2 relativistic magnetic-dipole matrix element in He+

When a beam of spin-polarized He+(2s1/2) ions is quenched by an electric field E, the emitted radiation intensity contains a left-right-asymmetry term proportional to Pk×E, where P is the spin-polarization vector and k is the observation direction. The resulting asymmetry is proportional to the relativistic magnetic dipole matrix element 1s1/2,1/2M1,02s 1/2,1/2. The measured asymmetry (2.935±0.337)×10-4 corresponds to the matrix element 1s1/2,1/2M1,02s 1/2,1/2 =-(0.2725±0.0313)α2eLatin small letter h with stroke/mc, in agreement with the theoretical value -0.2794α2eLatin small letter h with stroke/mc. The measurement provides a direct test of the relativistic corrections to the magnetic dipole transition operator. © 1986 The American Physical Society

Lifetime of the 2p state in He II

When a beam of spin-polarized metastable He+(2s12) ions is quenched by an electric field E\u27, the emitted radiation intensity contains an asymmetry term proportional to (kE)(P\u27k×E), where P\u27 is the spin-polarization vector and k is the direction of observation. The resulting asymmetry is nearly proportional to the level width of the 2p12 state in He+. The measured asymmetry 0.007 602 70.000 020 3 corresponds to a lifetime 2p=(0.99920.0026)×10-10 sec, in fair agreement with the theoretical value 2p=0.9972×10-10 sec. © 1983 The American Physical Society