1,540 research outputs found
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 . This indicates that
the flux density in the \textit{bulk} of normal domains can be
\textit{considerably} less than , in apparent contradiction with the long
established paradigm, stating that the normal phase is unstable below .
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
Understanding Archaeological Site Topography: 3D Archaeology of Archaeology
The current ubiquitous use of 3D recording technologies in archaeological fieldwork, for a large part due to the application of budget-friendly (drone) sensors and the availability of many low-cost image-based 3D modelling software packages, has exponentially increased the amount of 3D data of archaeological sites and landscapes. Various applications have advanced far beyond the experimental phase, such as the deployment of 3D surface recording for excavation interpretation, as a complementary data layer for prospection and as the basis for visualisation/presentation. Of particular attention here is the degree to which drone 3D recording can further advance the understanding of archaeological site topography. In this paper, current developments in the field of 3D recording will be discussed in the context of the ‘Archaeology of Archaeology’ approach, which is being developed at the University of Amsterdam. This paper is the result of a Round Table discussion at the CAA conference on April 5, 2023, in Amsterdam. The examples at the conference sessions clearly showed how beneficial it is when 3D recording techniques can be combined with other available information. In particular, the potential of old photographs was highlighted. Our experiences at Troy suggest that re-excavation of dumps and specific trenches and comparison of finds are also highly promising. In addition, considering the manifold possibilities of 3D hard- and software and the sheer quantity of the data available for a site such as Troy, several attendees to the session emphasized the necessity of a problem-oriented approach when researching and developing a platform as an access point, organising, and presenting collected information
Bubble size prediction in co-flowing streams
In this paper, the size of bubbles formed through the breakup of a gaseous
jet in a co-axial microfluidic device is derived. The gaseous jet surrounded by
a co-flowing liquid stream breaks up into monodisperse microbubbles and the
size of the bubbles is determined by the radius of the inner gas jet and the
bubble formation frequency. We obtain the radius of the gas jet by solving the
Navier-Stokes equations for low Reynolds number flows and by minimization of
the dissipation energy. The prediction of the bubble size is based on the
system's control parameters only, i.e. the inner gas flow rate , the outer
liquid flow rate , and the tube radius . For a very low gas-to-liquid
flow rate ratio () the bubble radius scales as , independently of the inner to outer viscosity
ratio and of the type of the velocity profile in the gas, which
can be either flat or parabolic, depending on whether high-molecular-weight
surfactants cover the gas-liquid interface or not. However, in the case in
which the gas velocity profiles are parabolic and the viscosity ratio is
sufficiently low, i.e. , the bubble diameter scales as
, with smaller than 1/2
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
He+ 2p state lifetime by a quenching-asymmetry measurement
An interference asymmetry in the angular distribution of the Ly quenching radiation emitted by He+ ions in the metastable 2s1/2 state is measured to high precision to obtain the lifetime of the 2p1/2 state. The derived lifetime of (0.997 170.000 75)×10-10 s is the most accurate available for a fundamental atomic system. A detailed discussion of systematic corrections is included. The result is in good agreement with theory, thereby confirming the theory of radiative transition probabilities to 0.075%, and indicating that differences between theory and experiment for the alkali metals must be due to either inadequate wave functions or experimental errors. © 1992 The American Physical Society
Improved anisotropy measurement of the Lamb shift in He+
An improved anisotropy measurement of the Lamb shift is obtained by means of a new method for the high-precision measurement of light intensities. The photon-counting techniques used in our previous work [Phys. Rev. A 20, 1299 (1979)] are replaced by the direct measurement of photoelectron currents with high-precision electrometers. Our new value for the Lamb shift in He+ is 14 041.91.5 MHz. This agrees with the earlier microwave resonance measurement of Lipworth and Novick [Phys. Rev. 108, 1434 (1957)], but lies clearly below the more recent measurement by Narasimham and Strombotne [Phys. Rev. A 4, 14 (1971)]. © 1987 The American Physical Society
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