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  • 1990-1994  (7)
  • 1991  (7)
  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Applied physics 52 (1991), S. 277-280 
    ISSN: 1432-0649
    Keywords: 42.55 Fn ; 41.80 Dd ; 52.80 Tn
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Experimental investigations on an e-beam sustained near infrared Ar:Xe laser have been carried out to determine the intrinsic efficiency at optimized conditions. A parametric study at different sustainer currents reveals a maximum output energy depending on current density. Up to 8 bar the optimized laser output power per unit volume increases linearly with 1.1MW/1 bar. Intrinsic efficiencies of up to about 8% are feasible.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Applied physics 52 (1991), S. 336-340 
    ISSN: 1432-0649
    Keywords: 34.80 D ; 41.80 Dd ; 42.55 F
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract In order to study the kinetic mechanism of the e-beam pumped Ar/Xe laser, the temporal profiles of individual laser lines during multiline oscillation have been measured as a function of power deposition (1–12MW/cm3) and gas laser pressure (2–14 bar) using a short pulse (30 ns) coaxial electron beam as excitation source. It was found that the optimum output energy at each pressure was obtained at the same specific power deposition. Strong line competition has been observed between the 2.65 and 1.73 μm transitions. In order to explain our results we suggest that besides electron collision mixing (ECM) between the 5d and 6p levels of Xe, there is also a redistribution between all 6p levels which strongly favours the lower levels at higher pumping densities.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The LDEF spacecraft was launched by the space shuttle Challenger on 7 April 1984 into a nearly circular orbit with an inclination of 28.5° and an altitude of 480 km. It was retrieved by the space shuttle Columbia on 12 January 1990 at an altitude of 310km. Because of its large mass, long ...
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1432-1084
    Keywords: Magnetic resonance ; Magnetic resonance-pulse sequences ; Magnetic resonance angiography ; Carotid arteries
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Three-dimensional (3D) time-of-flight methods are used to study anatomy and pathology of the supra-aortic arteries because they are quick and optimal for fast-flow conditions. Although highest signal intensities can be obtained by orientating the sections perpendicular to the long axis of the artery (axial), sagittal and/or coronal slice orientations cover the regions of interest with smaller volumes and therefore give adequate information in less time. Sagittal and coronal time-of-flight magnetic resonance angiography (MRA) gave excellent results (sensitivity 92.3%, specificity 85.7%, accuracy 90.9%) compared with intra-arterial digital subtraction angiography (DSA) in 30 patients, when coronal and sagittal acquisition were combined for final diagnosis. These values decreased to 69.6%/57.1%/66.7% for coronal and 83.6%/78.6%/81.7% for sagittal sections. Reasons for the variable extent of signal dropout at the site of a stenosis and for the different appearances of post-stenotic slow flow in the various planes are explained by T1 phenomena and intravoxel phase dispersion due to variable parameter settings.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Graphite-epoxy cross-ply laminates generally show multiple fracture of the transverse ply at higher applied stress. This phenomenon is described by means of a Monte Carlo simulation method based on the assumption that the strength of the transverse ply obeys a two-parameter Weibull distribution function. The main results show that the smaller the scatter of strength of the 90°-ply (i.e. the larger the shape parameter at a constant mean strength of the Weibull distribution), the higher becomes the threshold for the multiple fracture to occur, and the more rapidly the length of 90°-ply segments decreases with increasing applied stress once multiple fracture takes place. The methods to determine the shape and scale parameters of the Weibull distribution for the strength of the 90°-ply proposed by Manderset al. and Peters are proved to be useful even for a small number of test specimens. When the interfacial bond strength between 0°- and 90°-plies is low, saturation of 90°-ply cracking occurs at higher applied stress. The stress-carrying capacity and stiffness of the composites as a whole are reduced by multiple fracture of the 90°-ply. This reduction is more pronounced at increasing applied stress or at a larger number of transverse cracks, especially when the interfacial bond strength is low.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Graphite-epoxy cross-ply laminates generally show multiple fracture of the transverse ply at higher applied stress. This phenomenon is described by means of a Monte Carlo simulation method based on the assumption that the strength of the transverse ply obeys a two-parameter Weibull distribution function. The main results show that the smaller the scatter of strength of the 90°-ply (i.e. the larger the shape parameter at a constant mean strength of the Weibull distribution), the higher becomes the threshold for the multiple fracture to occur, and the more rapidly the length of 90°-ply segments decreases with increasing applied stress once multiple fracture takes place. The methods to determine the shape and scale parameters of the Weibull distribution for the strength of the 90°-ply proposed by Manderset al. and Peters are proved to be useful even for a small number of test specimens. When the interfacial bond strength between 0°- and 90°-plies is low, saturation of 90°-ply cracking occurs at higher applied stress. The stress-carrying capacity and stiffness of the composites as a whole are reduced by multiple fracture of the 90°-ply. This reduction is more pronounced at increasing applied stress or at a larger number of transverse cracks, especially when the interfacial bond strength is low.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Journal of inherited metabolic disease 14 (1991), S. 831-832 
    ISSN: 1573-2665
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Type of Medium: Electronic Resource
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