2,829 research outputs found
Remotely controlled mirror of variable geometry for small angle x-ray diffraction with synchrotron radiation
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
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
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 -space.Comment: 13 pages, 4 figures, submitted to Phys Rev
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Correlated analyses of D- and 15N-rich carbon grains from CR2 chondrite EET 92042
Extract from introduction: Insoluble organic matter (IOM) and matrix from primitive carbonaceous chondrites carry isotope enrichments (?D?20000', ?15N?3200�) that are comparable to those in interplanetary dust particles [1, this work]. Hence, primitive organics that formed in the protosolar cloud (PSC) – or maybe in the cold outer regions of the protoplanetary disk – survived accretion and planetary processing on the asteroids, the parent bodies of the chondrites
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Correlated Microscale Isotope and Scanning Transmission X-Ray Analyses of Isotopically Anomalous Organic Matter from the CR2 Chondrite EET 92042
We discuss correlated examinations of organic matter from the CR2 chondrite EET 92042, using SIMS, STXM and other methods. We found a large, isotopically highly anomalous region of probable presolar origin that is C- and 13C-poor and 15N-rich
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Secondary ion mass spectrometry and x-ray absorption near-edge structure spectroscopy of isotopically anomalous organic matter from CR1 chondrites GRO 95577
We located interstellar organics from a CR1 chondrite with NanoSIMS and analyzed FIB-extracted sections with XANES. D-rich material appears not associated with a functional group, whereas 15N-rich matter shows some affinity to nitrile functionality
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The risk assessment of ERTMS-based railway systems from a cyber security perspective: Methodology and lessons learned
The impact that cyber issues might have on the safety and resilience of railway systems has been studied for more than five years by industry specialists and government agencies. This paper presents some of the work done by Adelard in this area, ranging from an analysis of potential vulnerabilities in the ERTMS specifications through to a high-level cyber security risk assessment of a national ERTMS implementation and detailed analysis of particular ERTMS systems on behalf of the GB rail industry. The focus of the paper is on our overall methodology for security-informed safety and hazard analysis. Lessons learned will be presented but of course our detailed results remain proprietary or sensitive and cannot be published
Data collection in protein crystallography: capillary effects and background corrections
Single-Particle Density of States of a Superconductor with a Spatially Varying Gap and Phase Fluctuations
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 of a model high-T
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: , with a small gap and large
superfluid density, and , with the opposite. If the regions are
randomly embedded in an host, the LDOS on the sites still has
a sharp coherence peak at , but the component does not, in
agreement with experiment. An ordered arrangement of regions leads to
oscillations in the LDOS as a function of energy. The model leads to a
superconducting transition temperature well below the pseudogap
temperature , and has a spatially varying gap at very low , both
consistent with experiments in underdoped Bi2212. Our calculated
LDOS shows coherence peaks for , in agreement with previous work considering phase but not amplitude
fluctuations in a homogeneous superconductor. Well above , the gap in the
LDOS disappears.Comment: 37 pages, 12 figures. Accepted by Phys. Rev. B. Scheduled Issue: 01
Nov 200
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