Much of modern research in turbulence requires high Reynolds and Rayleigh numbers. A collaborative effort involving researchers at the University of Oregon and at Yale University has investigated the use of cryogenic gaseous helium to study thermal convection, helium I to study turbulent flow through pipes and grids, and helium II for the study of superfluid grid turbulence. We have recently constructed and commissioned the first cryogenic wind tunnel operating with helium gas at 6K. Intense turbulence generates very small eddies which need to be resolved. Progress in this direction will be described. We have also been successful in implementing Particle Image Velocimetry at low temperatures and have applied it to the study of grid turbulence in helium I. The talk will conclude with a discussion of challenges and opportunities in this field in the future.
A selection of seemingly unrelated experiments on sold molecular hydrogen, cryogenic atomic hydrogen and high temperature superconductors are revisited, with the object of showing how one followed from the other. Along the way, the advantages (and disadvantages) of being a scientific gypsy will be pointed out.
Superconductor-insulator (SI) transitions in ultra-thin metal films, tuned
either by magnetic field or disorder, have attracted substantial attention
over the last decade because of the possibility that they are quantum
phase
transitions, and because in two dimensions, there is direct competition
between coherence effects associated with superconductivity and effects
associated with localization. The elegant bosonic picture of
superconductor-insulator transitions that was proposed some years ago and
appeared to explain the data, is a best only in qualitative agreement with
measurements, which suggest more complex behavior. A critical review of
the experiments along with a survey of theory will be presented.
*Work supported by the Condensed Matter Physics Program of the NSF and
performed in collaboration with B. G. Orr, H. Jaeger, D. Haviland, Y. Liu,
G. Martinez-Arizala, N. Markovic, C. Christiansen, and L. Hernandez.