arXiv subjects

Kerry Kuehn

Publications and source records attributed to Kerry Kuehn.

5 recordsLinked to original sources

arXiv2011

Mutual Friction in Superfluid He^4 Near the λ-line

We present experimental results for the thermal resistivity ρ of superfluid He^4 along several isobars between saturated vapor pressure and the melting pressure. The measurements are for the temperature range 1 - T_c(q)/T_λ < t < 2{\times}10^{-5} and the heat-flux range 3 < q < 70 μW/cm^2. Here t {\equiv} 1-T/T_λ, T_λ is the transition temperature in the limit of zero q, and T_c is the transition temperature at finite q. The data suggest that the resistivity has an incipient singularity at T_λ which can be described by the power law ρ = (t/t0)^{-(mν+α)} where t0 = (q/q0)^x. However, the singularity is supplanted by the transition to a more highly dissipative phase at T_c(q) < T_λ. The results suggest a mild dependence of mν + α on P, but can be described quite well by mν + α = 2.76, x = 0.89, and q_0 = q_{0,0} - q_{0,1}P with q_{0,0} = 401 W/cm^2 and q_{0,1} = -5.0 W /{cm^2-bar}. The results imply that the Gorter-Mellink mutual friction exponent m has a value close to 3.46 and is distinctly larger than the classical value m = 3. We suggest that the reason for this may be found in the nature of the counterflow close to T_λ, which is expected to involve turbulent normalfluid flow.

cond-mat.other↗

arXiv2010

Vortex ring refraction at large Froude numbers

We have experimentally studied the impact of an initially planar axisymmetric vortex ring, incident at an oblique angle, upon a gravity-induced interface separating two fluids of differing densities. After impact, the vortex ring was found to exhibit a variety of subsequent trajectories, which we organize according to both the incidence angle, $θ_i$, and the interface strength, defined as the ratio of the Atwood and Froude numbers, $A/F$. For grazing incidence angles ($θ_i \gtrsim 70$ deg.) vortices either penetrate or reflect from the interface, depending on whether the interface is weak or strong. In some cases, reflected vortices execute damped oscillations before finally disintegrating. For smaller incidence angles ($θ_i \lesssim 70$ deg.) vortices penetrate the interface. When there is a strong interface, these vortices are observed to curve back up toward the interface. When there is a weak interface, these vortices are observed to refract downward, away from the interface. The critical interface strength below which vortex ring refraction is observed is given by $\log_{10}{(A/F)}= -2.38 \pm 0.05$.

physics.flu-dyn↗

arXiv2007

Apparatus for real-time acoustic imaging of Rayleigh-Benard convection

We have designed and built an apparatus for real-time acoustic imaging of convective flow patterns in optically opaque fluids. This apparatus takes advantage of recent advances in two-dimensional ultrasound transducer array technology; it employs a modified version of a commercially available ultrasound camera, similar to those employed in non-destructive testing of solids. Images of convection patterns are generated by observing the lateral variation of the temperature dependent speed of sound via refraction of acoustic plane waves passing vertically through the fluid layer. The apparatus has been validated by observing convection rolls in both silicone oil and ferrofluid.

cond-mat.mtrl-sci↗

arXiv2007

Tidal pattern instabilities on multi-moon planets

The equilibrium tide-generating forces in the lunar orbital plane of a planet of radius R are calculated for the case of N moons of mass M_i orbiting the planet at instantaneous polar coordinates (D_i, α_i). For the case of a single moon, there are only two high tides. For the case of two moons, it is found that there can exist a critical lunar orbital distance at which two high tides become unstable with respect to formation of three high tides. Bifurcation diagrams are presented which depict how the angular positions of the high and low tides on the planet vary with the lunar distances and lunar separation angle. Tidal stability diagrams, which illustrate the stability regions for various tidal patterns as a function of lunar distances and lunar separation angle, are presented for various values of D_2/D_1 and M_2/M_1. Generally speaking, the aforementioned tidal instability, and hence the propensity for formation of three high tides on a two-moon planet, exists over a significant range of lunar distances and separation angles provided that M_2/M_1 \sim (D_2/D_1)^3. For the case of N>2 moons, the tidal stability diagram becomes more complex, revealing a diversity of potential tidal patterns.

physics.ao-ph↗

arXiv2001

Singularity in the boundary resistance between superfluid $^4$He and a solid surface

We report new measurements in four cells of the thermal boundary resistance $R$ between copper and $^4$He below but near the superfluid-transition temperature $T_λ$. For $10^{-7} \leq t \equiv 1 - T/T_λ\leq 10^{-4}$ fits of $R = R_0 t^{x_b} + B_0$ to the data yielded $x_b \simeq 0.18$, whereas a fit to theoretical values based on the renormalization-group theory yielded $x_b = 0.23$. Alternatively, a good fit of the theory to the data could be obtained if the {\it amplitude} of the prediction was reduced by a factor close to two. The results raise the question whether the boundary conditions used in the theory should be modified.

cond-mat↗