281 research outputs found

    Development of a perturbation generator for vortex stability studies

    Get PDF
    Theory predicts vortex instability when subjected to certain types of disturbances. It was desired to build a device which could introduce controlled velocity perturbations into a trailing line vortex in order to study the effects on stability. A perturbation generator was designed and manufactured which can be attached to the centerbody of an airfoil type vortex generator. Details of design tests and manufacturing of the perturbation generator are presented. The device produced controlled perturbation with frequencies in excess of 250 Hz. Preliminary testing and evaluation of the perturbation generator performance was conducted in a 4 inch cylindrical pipe. Observations of vortex shedding frequencies from a centerbody were measured. Further evaluation with the perturbation generator attached to the vortex generator in a 2 x 3 foot wind tunnel were also conducted. Hot-wire anemometry was used to confirm the perturbation generator's ability to introduce controlled frequency fluctuations. Comparison of the energy levels of the disturbances in the vortex core was made between locations 42 chord lengths and 15 chord lengths downstream

    Loss of histone methyltransferase Ezh2 stimulates an osteogenic transcriptional program in chondrocytes but does not affectcartilage development

    Get PDF
    Ezh2 is a histone methyltransferase that suppresses osteoblast maturation and skeletal development. We evaluated the roleof Ezh2 in chondrocyte lineage differentiation and endochondral ossification. Ezh2 was genetically inactivated in the mesenchymal, osteoblastic, and chondrocytic lineages in mice using the Prrx1-Cre,Osx1-Cre, and Col2a1-Cre drivers, respectively. Wild-type and conditional knockout mice were phenotypically assessed by grossmorphology, histology, and micro-CT imaging. Ezh2-deficient chondrocytes in micromass culture models were evaluated usingRNA-sequencing, histologic evaluation, and western blotting. Aged mice with Ezh2 deficiency were also evaluated for prematuredevelopment of osteoarthritis using radiographic analysis. Ezh2 deficiency in murine chondrocytes reduced bone density at 4 weeks of age, although caused no other gross developmentaleffects. Knockdown of Ezh2 in chondrocyte micromass cultures resulted in a global reduction in trimethylation of histone 3lysine 27 (H3K27me3) and altered differentiation in vitro. RNA-seq analysis revealed enrichment of an osteogenic gene expressionprofile in Ezh2 deficient chondrocytes. Joint development proceeded normally in the absence of Ezh2 in chondrocytes withoutinducing excessive hypertrophy or premature osteoarthritis in vivo. In summary, loss of Ezh2 reduced H3K27me3 levels, increased expression of osteogenic genes in chondrocytes, and resulted ina transient post-natal bone phenotype. Remarkably, Ezh2 activity is dispensable for normal chondrocyte maturation and endochondralossification in vivo, even though it appears to have a critical role during early stages of mesenchymal lineage-commitment

    Magnetic domain wall propagation under ferroelectric control

    Get PDF
    Control of magnetic domain walls (DWs) and their propagation is among the most promising development directions for future information-storage devices. The well-established tools for such manipulation are the spin-torque transfer from electrical currents and strain. The focus of this paper is an alternative concept based on the nonvolatile ferroelectric field effect on DWs in a ferromagnet with carrier-mediated exchange coupling. The integrated ferromagnet/ferroelectric structure yields two superimposed ferroic patterns strongly coupled by an electric field. Using this coupling, we demonstrate an easy-to-form, stable, nondestructive, and electrically rewritable switch on magnetic domain wall propagation. DOI: 10.1103/PhysRevB.86.23513

    Development of CVD diamond radiation detectors

    Get PDF
    Diamond is a nearly ideal material for detecting ionizing radiation. Its outstanding radiation hardness, fast charge collection and low leakage current allow a diamond detector to be used in high ra diation, high temperature and in aggressive chemical media. We have constructed charged particle detectors using high quality CVD diamond. Characterization of the diamond samples and various detect ors are presented in terms of collection distance, d=μEτd=\mu E \tau, the average distance electron-hole pairs move apart under the influence of an electric field, where μ\mu is the sum of carrier mo bilities, EE is the applied electric field, and τ\tau is the mobility weighted carrier lifetime. Over the last two years the collection distance increased from \sim 75 μ\mum to over 200 μ\mu m. With this high quality CVD diamond a series of micro-strip and pixel particle detectors have been constructed. These devices were tested to determine their position resolution and signal to n oise performance. Diamond detectors were exposed to large fluences of pions, protons and neutrons to establish their radiation hardness properties. The results of these tests and their correlati on with the characterization studies are presented

    Performance of irradiated CVD diamond micro-strip sensors

    Get PDF
    CVD diamond detectors are of interest for charged particle detection and tracking due to their high radiation tolerance. In this article we present, for the first time, beam test results from recently manufactured CVD diamond strip detectors and their behavior under low doses of electrons from a β\beta-source and the performance before and after intense (>1015/cm2>10^{15}/{\rm cm^2}) proton- and pion-irradiations. We find that low dose irradiations increase the signal-to-noise ratio (pumping of the signal) and slightly deteriorate the spatial resolution. Intense irradiations with protons (2.2×1015 p/cm22.2\times 10^{15}~p/{\rm cm^2}) lowers the signal-to-noise ratio slightly. Intense irradiation with pions (2.9×1015 π/cm22.9\times 10^{15}~\pi/{\rm cm^2}) lowers the signal-to-noise ratio more. The spatial resolution of the diamond sensors improves after irradiations
    corecore