Growth of shocked gaseous interfaces in a conical geometry

The results of experiments on Richtmyer-Meshkov instability growth of multimode initial perturbations on an air-sulfur hexafluoride (SF6) interface in a conical geometry are presented. The experiments are done in a relatively larger shock tube. A nominally planar interface is formed by sandwiching a polymeric membrane between wire-mesh frames. A single incident shock wave ruptures the membrane resulting in multimode perturbations. The instability develops from the action of baroclinically deposited vorticity at the interface. The visual thickness delta of the interface is measured from schlieren photographs obtained in each run. Data are presented for delta at times when the interface has become turbulent. The data are compared with the experiments of Vetter [Shock Waves 4, 247 (1995)] which were done in a straight test section geometry, to illustrate the effects of area convergence. It is found from schlieren images that the interface thickness grows about 40% to 50% more rapidly than in Vetter's experiments. Laser induced scattering is used to capture the air-helium interface at late times. Image processing of pictures is also used to determine the interface thickness in cases where it was not clear from the pictures and to obtain the dominant eddy-blob sizes in the mixing zone. Some computational studies are also presented to show the global geometry changes of the interface when it implodes into a conical geometry in both light-heavy and heavy-light cases

Membrane mediated aggregation of curvature inducing nematogens and membrane tubulation

The shapes of cell membranes are largely regulated by membrane associated, curvature active, proteins. We use a numerical model of the membrane with elongated membrane inclusions, recently developed by us, which posses spontaneous directional curvatures that could be different along and perpendicular to its long axis. We show that, due to membrane mediated interactions these curvature inducing membrane nematogens can oligomerize spontaneously, even at low concentrations, and change the local shape of the membrane. We demonstrate that for a large group of such inclusions, where the two spontaneous curvatures have equal sign, the tubular conformation and sometime the sheet conformation of the membrane are the common equilibrium shapes. We elucidate the factors necessary for the formation of these {\it protein lattices}. Furthermore, the elastic properties of the tubes, like their compressional stiffness and persistence length are calculated. Finally, we discuss the possible role of nematic disclination in capping and branching of the tubular membranes.Comment: 15pages, 8 figure

Controlling hysteresis in superconducting constrictions with a resistive shunt

We demonstrate control of the thermal hysteresis in superconducting constrictions by adding a resistive shunt. In order to prevent thermal relaxation oscillations, the shunt resistor is placed in close vicinity of the constriction, making the inductive current-switching time smaller than the thermal equilibration time. We investigate the current-voltage characteristics of the same constriction with and without the shunt-resistor. The widening of the hysteresis-free temperature range is explained on the basis of a simple model.Comment: 6 pages, 7 figures, including Supplementary Informatio

Electronic structure studies of Fe- ZnO nanorods by x-ray absorption fine structure

We report the electronic structure studies of well characterized polycrystalline Zn_{1-x}Fe_xO (x = 0.0, 0.01, 0.03, and 0.05) nanorods synthesized by a co-precipitation method through x-ray absorption fine structure (XAFS). X-ray diffraction (XRD) reveals that Fe doped ZnO crystallizes in a single phase wurtzite structure without any secondary phase. From the XRD pattern, it is observed that peak positions shift towards lower 2\theta value with Fe doping. The change in the peak positions with increase in Fe contents clearly indicates that Fe ions are replacing Zn ions in the ZnO matrix. Linear combination fittings (LCF) at Fe K-edge demonstrate that Fe is in mixed valent state (Fe3+/Fe2+) with a ratio of ~ 7:3 (Fe3+:Fe2+). XAFS data is successfully fitted to wurtzite structure using IFEFFIT and Artemis. The results indicate that Fe substitutes Zn site in the ZnO matrix in tetrahedral symmetry.Comment: 7 pages, 5 figures, 2 tables, regular articl

An analytical stability theory for Faraday waves and the observation of the harmonic surface response

We present an analytical stability theory for the onset of the Faraday instability, applying over a wide frequency range between shallow water gravity and deep water capillary waves. For sufficiently thin fluid layers the surface is predicted to occur in harmonic rather than subharmonic resonance with the forcing. An experimental confirmation of this result is given. PACS: 47.20.Ma, 47.20.Gv, 47.15.CbComment: 10 pages (LaTeX-file), 3 figures (Postscript) Submitted for publicatio