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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 60 (1989), S. 2471-2474 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: This article describes a high-resolution three-dimensional CT system which has been tested on the new wiggler beamline X-2 at the Stanford Synchrotron Radiation Laboratory. The present system is a rotate-only design which uses a virtual phase CCD array camera optically coupled to a high-resolution phosphor screen. The spatial resolution of this system is presently somewhat better than 10 μm (50 line pairs/mm at 20% contrast). This resolution is limited by the optical elements in the detector, and we are undertaking an effort to improve this resolution to 1 μm. Nevertheless, the spatial resolution offered by this design is sufficient to begin many studies of interest to materials research, such as, supported catalysts, composite materials, and crack growth and propagation.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Employing asymmetric Bragg reflection at the monochromator we obtain a wide and practically parallel synchrotron-radiation beam which, when combined with the use of a CCD detector, enables us to perform chemically specific, high-speed and high-resolution tomography. We present recent results obtained with this new method. The actual resolution achieved was determined from the measured line-spread function of the complete detection system which includes the CCD, the fluorescent screen, and the lens used for optical magnification. The modulation-transfer function (MTF) calculated from the line-spread function shows that with only twofold magnification and at 3% contrast detectability about 28 line pairs per mm are resolved. Extrapolating from this result we find that with an optical magnification of 7:1 about 100 line pairs per mm should be resolved. Ways to optimize the method further are discussed.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A beamline has been constructed at Stanford Synchrotron Radiation Laboratory (SSRL) whose radiation source is a multipole permanent magnet wiggler installed in a straight section of the SPEAR 3–3.5 GeV electron storage ring. The wiggler is a hybrid design that utilizes Nd–Fe alloy magnet material combined with Vanadium Permendur poles. It is approximately 2 m long and has 15 full wiggler periods. Its field is regulated by varying its gap height. It has a peak operating field, limited by the electron beam vacuum chamber vertical aperture, of 1.4 T. The beamline consists of vacuum, safety, and optical components capable of transporting photons to one hard x-ray (3–30 keV) end station, with provisions for implementing up to two additional branch lines. The existing hard x-ray branch can be focused by a Pt-coated toroidal mirror with a cutoff energy of approximately 22 keV. The experimental end station is serviced by a Hower–Brown type double crystal monochromator. The wiggler and beamline construction was completed in the fall of 1987 and was operated for a brief period for characterization and experimental use. We present design details and results of the initial characterization studies.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Materials Research 22 (1992), S. 121-152 
    ISSN: 0084-6600
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 5
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Synchrotron microtomography is a new technique which is capable of elemental, chemical, and structure sensitive imaging in three dimensions at resolutions better than 15 μm. This paper describes the first application of this new technique to the investigation of the morphology and elemental distribution of a supported catalyst. Using this new tool it was possible to obtain three-dimensional information from regions of the catalyst away from the vicinity of the damaged surface region of the sample. The technique allows the use of both computed tomographic (CT) cross sections as well as the development of a three-dimensional rendering of elements in a material, each of which allows visualization of different areas that would go unnoticed in normal radiographic or CT investigations.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 1921-1923 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A technique was developed to determine the spatial localization of radio-opaque resonant markers in newly formed bone by synchrotron x-ray microtomography. The resolution of the technique shows potential for three-dimensional tomographic mapping of bone mineral deposition, as an index of bone formation. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    PO Box 1354, 9600 Garsington Road, Oxford OX4 2XG, UK. : Blackwell Science Ltd
    Fatigue & fracture of engineering materials & structures 28 (2005), S. 0 
    ISSN: 1460-2695
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The fracture of bone is a health concern of increasing significance as the population ages. It is therefore of importance to understand the mechanics and mechanisms of how bone fails, both from a perspective of outright (catastrophic) fracture and from delayed/time-dependent (subcritical) cracking. To address this need, there have been many in vitro studies to date that have attempted to evaluate the relevant fracture and fatigue properties of human cortical bone; despite these efforts, however, a complete understanding of the mechanistic aspects of bone failure, which spans macroscopic to nanoscale dimensions, is still lacking. This paper seeks to provide an overview of the current state of knowledge of the fracture and fatigue of cortical bone, and to address these issues, whenever possible, in the context of the hierarchical structure of bone. One objective is thus to provide a mechanistic interpretation of how cortical bone fails. A second objective is to develop a framework by which fracture and fatigue results in bone can be presented. While most studies on bone fracture have relied on linear-elastic fracture mechanics to determine a single-value fracture toughness (e.g., Kc or Gc), more recently, it has become apparent that, as with many composites or toughened ceramics, the toughness of bone is best described in terms of a resistance-curve (R-curve), where the toughness is evaluated with increasing crack extension. Through the use of the R-curve, the intrinsic and extrinsic factors affecting its toughness are separately addressed, where ‘intrinsic’ refers to the damage processes that are associated with crack growth ahead of the tip, and ‘extrinsic’ refers to the shielding mechanisms that primarily act in the crack wake. Furthermore, fatigue failure in bone is presented from both a classical fatigue life (S/N) and fatigue-crack propagation (da/dN) perspective, the latter providing for an easier interpretation of fatigue micromechanisms. Finally, factors, such as age, species, orientation, and location, are discussed in terms of their effect on fracture and fatigue behaviour and the associated mechanisms of bone failure.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 24 (1991), S. 771-776 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Structural properties of organic aerogels were studied by ultra-small-angle X-ray scattering (USAXS) at the Synchrotron Radiation Laboratory HASYLAB at DESY, Hamburg, Germany. The organic aerogels were synthesized from the base-catalyzed sol–gel polymerization of resorcinol with formaldehyde (RF) followed by a supercritical drying process. RF aerogels are low-density materials with a solid matrix composed of interconnected colloidal-like particles. Scattering experiments were carried out using a crystal camera optimized for ultra-small-angle X-ray scattering with synchrotron radiation. The measured SAXS profiles revealed a scattering power depending upon synthetic conditions of the gels. RF aerogels were found to be homogeneous at length scales greater than 20 nm. From Guinier plots, radii of gyration Rg of 3–20 nm were computed. Rg appears to be a measure of the pore (cell) size. Although fractal silica aerogels show similar characteristics, fractal behavior of the organic aerogels is uncertain. These materials are best described as random aggregates of smooth colloidal like particles with open-cell porosity.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Applied composite materials 1 (1994), S. 325-331 
    ISSN: 1573-4897
    Keywords: Composite ; Percolation ; Chemical vapor infiltration (CVI) ; Porosity ; Tomography
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Three-dimensional x-ray microtomography has been used to visualize porosity in ceramic matrix composites during chemical vapor infiltration processing. The topology of percolating pores was determined in both 0°/90° and 0°/45° architectures. At densities greater than 75%, consolidation can be described with percolation theory.
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 1432-0630
    Keywords: 79.40 ; 79.60
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract Electron emission due to 1.06 and 0.35 μm laser excitation has been measured at several pulse lengths for a number of wide bandgap semiconductors and insulators. The dependence on fluence and wavelength is consistent with multiphoton excitation across the bandgap. The work functions of the materials investigated do not appear to influence the rate-limiting multiphoton excitation process.
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