182 research outputs found
The saturation of decaying counterflow turbulence in helium II
We are concerned with the problem of the decay of a tangle of quantized
vortices in He II generated by a heat current. Direct application of Vinen's
equation yields the temporal scaling of vortex line density .
Schwarz and Rozen [Phys. Rev. Lett. {\bf 66}, 1898 (1991); Phys. Rev. B {\bf
44}, 7563 (1991)] observed a faster decay followed by a slower decay. More
recently, Skrbek and collaborators [Phys. Rev. E {\bf 67}, 047302 (2003)] found
an initial transient followed by the same classical scaling observed
in the decay of grid-generated turbulence. We present a simple theoretical
model which, we argue, contains the essential physical ingredients, and
accounts for these apparently contradictory results.Comment: 19 pages, 5 figure
Scattering length of Andreev reflection from quantized vortices in He-
Andreev reflection of thermal quasiparticles from quantized vortices is an
important technique to visualize quantum turbulence in low temperature
He-. We revisit a problem of Andreev reflection from the isolated,
rectilinear vortex line. For quasiparticle excitations whose impact parameters,
defined as distances of the closest approach to the vortex core, do not exceed
some arbitrary value, , we calculate exactly the reflected fraction of the
total flux of excitations incident upon the vortex in the direction orthogonal
to the vortex line. We then define and calculate exactly, as a function of ,
the scattering length, that is the scattering cross-section per unit length of
the vortex line. We also define and calculate the scattering lengths for the
flux of energy carried by thermal excitations, and for the net energy flux
resulting from a (small) temperature gradient, and analyze the dependence of
these scattering lengths on temperature.Comment: 8 pages, 4 figure
Molecular Modeling of Protein Structure, Biology of Disease and Clinical Electroretinography in Human X-Linked Retinoschisis (XLRS)
Coherent vortex structures in quantum turbulence
This report addresses an important question discussed by the quantum
turbulence community during the last decade: do quantized vortices form, in
zero-temperature superfluids, coherent structures similar to vortex tubes in
ordinary, viscous turbulence? So far the evidence provided by numerical
simulations is that bundles of quantized vortices appear in finite-temperature
superfluids, but from the interaction with existing coherent structures in the
turbulent (viscous) normal fluid, rather than due to the intrinsic superfuid
dynamics. In this report we show that, in very intense quantum turbulence
(whose simulation was made possible by a tree algorithm), the vortex tangle
contains small coherent vortical structures (bundles of quantized vortices)
which arise from the Biot-Savart dynamics alone, and which are similar to the
coherent structures observed in classical viscous turbulence.Comment: 6 pages, 6 figure
Spherical geometry and integrable systems
We prove that the cosine law for spherical triangles and spherical tetrahedra
defines integrable systems, both in the sense of multidimensional consistency
and in the sense of dynamical systems.Comment: 15 pages, 5 figure
- …