2,829 research outputs found

    Remotely controlled mirror of variable geometry for small angle x-ray diffraction with synchrotron radiation

    Get PDF
    A total-reflecting mirror of 120-cm length was designed and built to focus synchrotron radiation emanating from the electron-positron storage ring at the Stanford Linear Accelerator Center (SPEAR). The reflecting surface is of unpolished float glass. The bending and tilt mechanism allows very fine control of the curvature and selectability of the critical angle for wavelengths ranging from 0.5 to 3.0 Ã…. Elliptical curvature is used to minimize aberrations. The mirror is placed asymmetrically onto the ellipse so as to achieve a tenfold demagnification of the source. The bending mechanism reduces nonelastic deformation (flow) and minimizes strains and stresses in the glass despite its length. Special design features assure stability of the focused image. The mirror reduces the intensity of shorter wavelength harmonics by a factor of approximately 100

    Recent development in the design, testing and impact-damage tolerance of stiffened composite panels

    Get PDF
    Structural technology of laminated filamentary-composite stiffened-panel structures under combined inplane and lateral loadings is discussed. Attention is focused on: (1) methods for analyzing the behavior of these structures under load and for determining appropriate structural proportions for weight-efficient configurations; and (2) effects of impact damage and geometric imperfections on structural performance. Recent improvements in buckling analysis involving combined inplane compression and shear loadings and transverse shear deformations are presented. A computer code is described for proportioning or sizing laminate layers and cross-sectional dimensions, and the code is used to develop structural efficiency data for a variety of configurations, loading conditions, and constraint conditions. Experimental data on buckling of panels under inplane compression is presented. Mechanisms of impact damage initiation and propagation are described

    Magnonic Crystal with Two-Dimensional Periodicity as a Waveguide for Spin Waves

    Get PDF
    We describe a simple method of including dissipation in the spin wave band structure of a periodic ferromagnetic composite, by solving the Landau-Lifshitz equation for the magnetization with the Gilbert damping term. We use this approach to calculate the band structure of square and triangular arrays of Ni nanocylinders embedded in an Fe host. The results show that there are certain bands and special directions in the Brillouin zone where the spin wave lifetime is increased by more than an order of magnitude above its average value. Thus, it may be possible to generate spin waves in such composites decay especially slowly, and propagate especially large distances, for certain frequencies and directions in k{\bf k}-space.Comment: 13 pages, 4 figures, submitted to Phys Rev

    Single-Particle Density of States of a Superconductor with a Spatially Varying Gap and Phase Fluctuations

    Get PDF
    Recent experiments have shown that the superconducting energy gap in some cuprates is spatially inhomogeneous. Motivated by these experiments, and using exact diagonalization of a model d-wave Hamiltonian, combined with Monte Carlo simulations of a Ginzburg-Landau free energy functional, we have calculated the single-particle density of states LDOS(ω,r)(\omega,r) of a model high-Tc_c superconductor as a function of temperature. Our calculations include both quenched disorder in the pairing potential and thermal fluctuations in both phase and amplitude of the superconducting gap. Most of our calculations assume two types of superconducting regions: α\alpha, with a small gap and large superfluid density, and β\beta, with the opposite. If the β\beta regions are randomly embedded in an α\alpha host, the LDOS on the α\alpha sites still has a sharp coherence peak at T=0T = 0, but the β\beta component does not, in agreement with experiment. An ordered arrangement of β\beta regions leads to oscillations in the LDOS as a function of energy. The model leads to a superconducting transition temperature TcT_c well below the pseudogap temperature Tc0T_{c0}, and has a spatially varying gap at very low TT, both consistent with experiments in underdoped Bi2212. Our calculated LDOS(ω,r)(\omega,r) shows coherence peaks for TTcT T_c, in agreement with previous work considering phase but not amplitude fluctuations in a homogeneous superconductor. Well above TcT_c, the gap in the LDOS disappears.Comment: 37 pages, 12 figures. Accepted by Phys. Rev. B. Scheduled Issue: 01 Nov 200
    • …
    corecore