Investigation of magnetic field induced textural changes in superfluid 3He–A and of the anisotropy of viscosity, superfluid density, and sound propagation

1987 ◽  
Vol 65 (11) ◽  
pp. 1486-1493 ◽  
Author(s):  
J. R. Hook ◽  
A. D. Eastop ◽  
E. Faraj ◽  
S. G. Gould ◽  
H. E. Hall
Keyword(s):  
Magnetic Field ◽  
Sound Propagation ◽  
Superfluid 3He ◽  
Superfluid Density ◽  
Normal Phase ◽  
Torsional Oscillator ◽  
Sound Attenuation ◽  
Slab Geometry ◽  
Textural Changes

Textural changes induced by a magnetic field in dipole-locked superfluid 3He–A in a slab geometry have been observed and agree well with the theoretically predicted changes. In one set of observations, ultrasound transmission at 15.15 MHz across a slab 2 mm wide was used as the probe of the texture, and in another set of measurements the textural changes were inferred from the behaviour of a torsional oscillator containing a slab of thickness 105 μm. From the former set of observations, we deduced the anisotropy of the sound attenuation and velocity, and from the latter we calculated the anisotropy of the viscosity and the superfluid density. In both experiments the field, perpendicular to the slab, that caused instability of the uniform texture was smaller than that theoretically predicted. Observations on the A phase after warming from the B phase exhibited very different behaviour from those made after cooling from the normal phase.

scholarly journals Acoustic Signatures of the Phases and Phase Transitions in the Blume Capel Model with Random Crystal Field

2018 ◽  
Vol 2018 ◽  
pp. 1-13
Author(s):  
Gul Gulpinar
Keyword(s):  
High Frequency ◽  
Sound Propagation ◽  
Ultrasonic Attenuation ◽  
Experimental Studies ◽  
Power Laws ◽  
Sound Attenuation ◽  
Irreversible Processes ◽  
Acoustic Signatures ◽  
Sound Dispersion ◽  
Good Agreement

Sound propagation in the Blume Capel model with quenched diluted single-ion anisotropy is investigated. The sound dispersion relation and an expression for the ultrasonic attenuation are derived with the aid of the method of thermodynamics of irreversible processes. A frequency-dependent dispersion minimum that is shifted to lower temperatures with rising frequency is observed in the ordered region. The thermal and sound frequency (ω) dependencies of the sound attenuation and effect of the Onsager rate coefficient are studied in low- and high-frequency regimes. The results showed that ωτ≪1 and ωτ≫1 are the conditions that describe low- and high-frequency regimes, where τ is the single relaxation time diverging in the vicinity of the critical temperature. In addition, assuming a linear coupling of sound wave with the order parameter fluctuations in the system and ε as the temperature distance from the critical point, we found that the sound attenuation follows the power laws α(ω,ε)~ω2ε-1 and α(ω,ε)~ω0ε1 in the low- and high-frequency regions, while ε→0. Finally, a comparison of the findings of this study with previous theoretical and experimental studies is presented and it is shown that a good agreement is found with our results.

scholarly journals Self-Consistent Models for Small Photospheric Flux Tubes

1983 ◽  
Vol 102 ◽  
pp. 67-71
Author(s):  
W. Deinzer ◽  
G. Hensler ◽  
D. Schmitt ◽  
M. Schüssler ◽  
E. Weisshaar
Keyword(s):  
Magnetic Field ◽  
Flux Tube ◽  
Energy Transport ◽  
Numerical Study ◽  
Momentum Equation ◽  
Mhd Equations ◽  
Compressible Medium ◽  
Solar Photosphere ◽  
Slab Geometry ◽  
Element Technique

We give a short summary of some results of a numerical study of magnetic field concentrations in the solar photosphere and upper convection zone. We have developed a 2D time dependent code for the full MHD equations (momentum equation, equation of continuity, induction equation for infinite conductivity and energy equation) in slab geometry for a compressible medium. A Finite-Element-technique is used. Convective energy transport is described by the mixing-length formalism while the diffusion approximation is employed for radiation. We parametrize the inhibition of convective heat flow by the magnetic field and calculate the material functions (opacity, adiabatic temperature gradient, specific heat) self-consistently. Here we present a nearly static flux tube model with a magnetic flux of ∼ 1018 mx, a depth of 1000 km and a photospheric diameter of ∼ 300 km as the result of a dynamical calculation. The influx of heat within the flux tube at the bottom of the layer is reduced to 0.2 of the normal value. The mass distribution is a linear function of the flux function A: dm(A)/dA = const. Fig. 1 shows the model: Isodensities (a), fieldlines (b), isotherms (c) and lines of constant continuum optical depth (d) are given. The “Wilson depression” (height difference between τ = 1 within and outside the tube) is ∼ 150 km and the maximum horizontal temperature deficit is ∼ 3000 K. Field strengths as function of x for three different depths and as function of depth along the symmetry axis are shown in (e) and (f), respectively. Note the sharp edge of the tube.

scholarly journals EVALUATION OF SEVERAL NONREFLECTING COMPUTATIONAL BOUNDARY CONDITIONS FOR DUCT ACOUSTICS

1995 ◽  
Vol 03 (04) ◽  
pp. 327-342 ◽  
Author(s):  
WILLIE R. WATSON ◽  
WILLIAM E. ZORUMSKI ◽  
STEVE L. HODGE
Keyword(s):  
Boundary Condition ◽  
Boundary Conditions ◽  
Sound Propagation ◽  
Sparse Matrix ◽  
Nonlocal Boundary Condition ◽  
Nonlocal Boundary ◽  
Substantial Reduction ◽  
Sound Attenuation ◽  
Interior Solution ◽  
Duct Acoustics

Several nonreflecting computational boundary conditions that meet certain criteria and have potential applications to duct acoustics are evaluated for their effectiveness. The same interior solution scheme, grid, and order of approximation are used to evaluate each condition. Sparse matrix solution techniques are applied to solve the matrix equation resulting from the discretization. Modal series solutions for the sound attenuation in an infinite duct are used to evaluate the accuracy of each nonreflecting boundary condition. The evaluations are performed for sound propagation in a softwall duct, for several sources, sound frequencies, and duct lengths. It is shown that a recently developed nonlocal boundary condition leads to sound attenuation predictions considerably more accurate than the local ones considered. Results also show that this condition is more accurate for short ducts. This leads to a substantial reduction in the number of grid points when compared to other nonreflecting conditions.

Parametric Study on Rectangular Sonic Crystal

2012 ◽  
Vol 152-154 ◽  
pp. 281-286 ◽  
Author(s):  
Arpan Gupta ◽  
Kian Meng Lim ◽  
Chye Heng Chew
Keyword(s):  
Band Gap ◽  
Periodic Structure ◽  
Parametric Study ◽  
Sound Propagation ◽  
Periodic Structures ◽  
Sound Attenuation ◽  
Experimental Results ◽  
Center Frequency ◽  
Sonic Crystal ◽  
Sonic Crystals

Sonic crystals are periodic structures made of sound hard scatterers which attenuate sound in a range of frequencies. For an infinite periodic structure, this range of frequencies is known as band gap, and is determined by the geometric arrangement of the scatterers. In this paper, a parametric study on rectangular sonic crystal is presented. It is found that geometric spacing between the scatterers in the direction of sound propagation affects the center frequency of the band gap. Reducing the geometric spacing between the scatterers in the direction perpendicular to the sound propagation helps in better sound attenuation. Such rectangular arrangement of scatterers gives better sound attenuation than the regular square arrangement of scatterers. The model for parametric study is also supported by some experimental results.

Sound Propagation in Semimetals under Strong Magnetic Field

1971 ◽  
Vol 31 (5) ◽  
pp. 1306-1312 ◽  
Author(s):  
Michisuke Kobayashi ◽  
Kazuo Yamada
Keyword(s):  
Magnetic Field ◽  
Strong Magnetic Field ◽  
Sound Propagation

Bifurcation to vortex solutions in superconducting films

1997 ◽  
Vol 8 (2) ◽  
pp. 125-148 ◽  
Author(s):  
T. BOECK ◽  
S. J. CHAPMAN
Keyword(s):  
Magnetic Field ◽  
Superconducting Films ◽  
Leading Order ◽  
Nonlinear Stability Analysis ◽  
Slab Geometry ◽  
Weakly Nonlinear ◽  
Double Eigenvalue ◽  
Wide Range ◽  
Vortex Solutions ◽  
Parameter Values

The bifurcation from a normally conducting state to a superconducting state in a decreasing magnetic field is studied for a slab geometry. The leading eigenvalue is a double eigenvalue, leading to a rich structure of possible behaviours. A weakly-nonlinear stability analysis is performed, and the possible responses of the material are classified. Finally, the leading-order equations are solved numerically for a wide range of parameter values to determine which of these behaviours will occur in practice.

Magnetic Field Dependence of the A-like to B-like Transition of Superfluid 3He in Aerogel

2009 ◽  
Vol 158 (1-2) ◽  
pp. 170-175
Author(s):  
B. H. Moon ◽  
N. Masuhara ◽  
P. Bhupathi ◽  
M. Gonzalez ◽  
M. W. Meisel ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Field Dependence ◽  
Magnetic Field Dependence ◽  
Superfluid 3He

Orbital Viscosity in Superfluid 3He-B in a Magnetic Field

2005 ◽  
Vol 138 (3-4) ◽  
pp. 771-776 ◽  
Author(s):  
S. N. Fisher ◽  
N. Suramlishvili
Keyword(s):  
Magnetic Field ◽  
Superfluid 3He
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