Normal-state conductivity in underdoped La_{2-x}Sr_xCuO_4 thin films: Search for nonlinear effects related to collective stripe motion

We report a detailed study of the electric-field dependence of the normal-state conductivity in La_{2-x}Sr_xCuO_4 thin films for two concentrations of doped holes, x=0.01 and 0.06, where formation of diagonal and vertical charged stripes was recently suggested. In order to elucidate whether high electric fields are capable of depinning the charged stripes and inducing their collective motion, we have measured current-voltage characteristics for various orientations of the electric field with respect to the crystallographic axes. However, even for the highest possible fields (~1000 V/cm for x=0.01 and \~300 V/cm for x=0.06) we observed no non-linear-conductivity features except for those related to the conventional Joule heating of the films. Our analysis indicates that Joule heating, rather than collective electron motion, may also be responsible for the non-linear conductivity observed in some other 2D transition-metal oxides as well. We discuss that a possible reason why moderate electric fields fail to induce a collective stripe motion in layered oxides is that fairly flexible and compressible charged stripes can adjust themselves to the crystal lattice and individual impurities, which makes their pinning much stronger than in the case of conventional rigid charge-density waves.Comment: 10 pages, 10 figures, accepted for publication in Phys. Rev.

Regimes of Two-Phase Flow in Short Rectangular Channel

En ligne: http://www.springerlink.com/content/e76470515h2t7271/info:eu-repo/semantics/publishe

Tomographic PIV measurements in a swirling jet flow

The present work is devoted to the application of the Tomographic PIV technique to study coherent structures in a swirling turbulent jet. The aim of the paper is to study the possibilities of caring out tomographic PIV measurements with the large depth of a volume configuration in the swirling jet setup. It is recognized that an extension of the Tomo PIV technique to a large depth of view along light deficiency gives a set of problems linked with the optical opacity limit, the uncertainty of reconstruction by few projections and the increasing of the ghost particles number. Thus, the paper reports results of comparative study of the mean flow characteristics by Tomo PIV and Stereo PIV. The measurements were carried out by Tomo PIV and Stereo PIV techniques for the same object and under the same experimental conditions. From the analysis of the obtained results, the volumetric to planar comparison showed acceptable correspondence through all common measurement points for mean velocity and satisfactory correspondence of the velocity fluctuations intensity. The comparison of coherent structures detected by proper orthogonal decomposition (POD) analysis of 3D velocity distributions with large-scale vortices in a set of the instantaneous velocity fields with the decent spatial resolution (1.5 mm) was performed. The instantaneous data revealed the presence of the double vortex helix at the inner shear layer and appearance of an additional secondary helical vortex in the outer mixing layer. The phase-averaged vortex structure from POD data resolves only one vortex helix in the outer shear layer and a thick screw or drill like structure at the axis of the jet without resolving distinct double helix of vortex filaments, detected in the instant 3D velocity distributions

IFN-γ primes macrophage responses to bacterial DNA

Macrophages recognize and are activated by unmethylated CpG motifs in bacterial DNA, Here we demonstrate that production of nitric oxide (NO) from murine RAW 264 macrophages and bone marrow-derived macrophages (BMM) in response to bacterial DNA is absolutely dependent on interferon-gamma (IFN-gamma) priming. Similarly, arginine uptake and expression of the inducible nitric oxide synthase (iNOS) gene in response to bacterial DNA in BMM occurred only after IFN-gamma priming, In contrast, mRNA for the cationic amino acid transporter, CAT2, was induced by plasmid DNA alone, and priming with IFN-gamma had no effect on this response. Tumor necrosis factor-alpha (TNF-alpha) release from RAW 264 and BMM in response to bacterial DNA was augmented by IFN-gamma pretreatment, In a stably transfected HIV-1 long terminal repeat (LTR) luciferase RAW 264 cell line, IFN-gamma and bacterial DNA synergized in activation of the HIV-1 LTR. Bacterial DNA has been shown to induce IFN-gamma production in vivo as an indirect consequence of interleukin-12 (IL-12) and TNF-alpha production from macrophages, The results herein suggest the existence of a self-amplifying loop that may have implications for therapeutic applications of bacterial DNA