Scaling Behavior of Quasi-One-Dimensional Vortex Avalanches in Superconducting Films

Scaling behaviour of dynamically driven vortex avalanches in superconducting YBa$_{2}$Cu$_{3}$O$_{7-\delta}$ films deposited on tilted crystalline substrates has been observed using quantitative magneto-optical imaging. Two films with different tilt angles are characterized by the probability distributions of avalanche size in terms of the number of moving vortices. It is found in both samples that these distributions follow power-laws over up to three decades, and have exponents ranging between 1.0 and 1.4. The distributions also show clear finite-size scaling, when the system size is defined by the depth of the flux penetration front -- a signature of self-organized criticality. A scaling relation between the avalanche size exponent and the fractal dimension, previously derived theoretically from conservation of the number of magnetic vortices in the stationary state and shown in numerical simulations, is here shown to be satisfied also experimentally.Comment: 7 pages, 5 figure

Nonlinear acousto-electric transport in a two-dimensional electron system

We study both theoretically and experimentally the nonlinear interaction between an intense surface acoustic wave and a two-dimensional electron plasma in semiconductor-piezocrystal hybrid structures. The experiments on hybrid systems exhibit strongly nonlinear acousto-electric effects. The plasma turns into moving electron stripes, the acousto-electric current reaches its maximum, and the sound absorption strongly decreases. To describe the nonlinear phenomena, we develop a coupled-amplitude method for a two-dimensional system in the strongly nonlinear regime of interaction. At low electron densities the absorption coefficient decreases with increasing sound intensity, whereas at high electron density the absorption coefficient is not a monotonous function of the sound intensity. High-harmonic generation coefficients as a function of the sound intensity have a nontrivial behavior. Theory and experiment are found to be in a good agreement.Comment: 27 pages, 6 figure

Genes Required for Growth at High Hydrostatic Pressure in Escherichia coli K-12 Identified by Genome-Wide Screening

Despite the fact that much of the global microbial biosphere is believed to exist in high pressure environments, the effects of hydrostatic pressure on microbial physiology remain poorly understood. We use a genome-wide screening approach, combined with a novel high-throughput high-pressure cell culture method, to investigate the effects of hydrostatic pressure on microbial physiology in vivo. The Keio collection of single-gene deletion mutants in Escherichia coli K-12 was screened for growth at a range of pressures from 0.1 MPa to 60 MPa. This led to the identification of 6 genes, rodZ, holC, priA, dnaT, dedD and tatC, whose products were required for growth at 30 MPa and a further 3 genes, tolB, rffT and iscS, whose products were required for growth at 40 MPa. Our results support the view that the effects of pressure on cell physiology are pleiotropic, with DNA replication, cell division, the cytoskeleton and cell envelope physiology all being potential failure points for cell physiology during growth at elevated pressure

Effect of Vacuum Annealing on Orientation of Fluorite Films on Tilted-Axes Substrates

CeO2 and Y:ZrO2 (YSZ) fluorite films were deposited on NdGaO3 (NGO) tilted-axes substrates by pulsed laser deposition technique after oxygen or vacuum annealing, the orientation features of the resulting films were studied. The fluorite films on oxygen-annealed substrates showed good agreement with the graphoepitaxial growth mechanism. An excessive tilt over the calculated values is observed for substrate tilt angles of 10°–15°, presumably as a result of generation of regular dislocations. On vacuum-annealed substrates the YSZ films showed no additional tilt, instead a re-orientation towards (012) and (013) crystallographic planes of the film is observed for tilt angles 13°–15° and 18°–20°, respectively. Similar effects are observed for CeO2 films after relaxation at critical thickness. The CeO2 films on vacuum annealed substrates are seeded with alignment of (111) plane with the (110) plane of the substrate instead of standard (001) CeO2 plane. Some part of the CeO2 grains is oriented with the (111) plane along the substrate surface. The angular vicinity of a small-index crystallographic plane to the graphoepitaxial tilt value may result in an “accidental” epitaxial alignment.</p