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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 6 (1999), S. 837-845 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The linear and nonlinear stability of a nonmonotonic q profile is examined using a reduced set of magnetohydrodynamic (MHD) equations with an equilibrium, sheared toroidal flow. The reversed shear profile is shown to be unstable to a rich variety of resistive MHD modes including pressure-driven instabilities and tearing instabilities possessing a tearing/interchange character at low Lundquist number, S, and taking on a double/triple tearing structure at high S. Linear calculations show that the destabilizing effect of toroidal velocity shear on tearing modes is enhanced at finite pressure. In addition, this velocity shear decreases the stabilizing effect of finite pressure seen previously for tearing modes at high S. Nonlinear calculations show the generation of a large, m=1, n=0, Reynolds-stress-driven poloidal flow in the absence of significant flow damping. Calculations in which the poloidal flow was heavily damped show that sub-Alfvénic, sheared toroidal flows have a minimal effect on weakly coupled, localized instabilities. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 1171-1179 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this work, a unified closure for the conductive electron heat flux along magnetic field lines is derived and examined. Both free-streaming and collisional pitch-angle scattering of electrons are present in the drift kinetic equation which is solved using an expansion in pitch-angle eigenfunctions (Legendre polynomials). The closure takes the form of a generic integral operator involving the electron temperature variation along a magnetic field line and the electron speed. Derived for arbitrary collisionality, the heat flux closure may be written in forms resembling previous collisional and collisionless expressions. Electrons with two to three times the thermal speed are shown to carry heat for all collisionalities and thermal electrons make an important contribution to the heat flow in regimes of moderate to low collisionality. As a practical application, the flow of electron heat along a chaotic magnetic field is calculated in order to highlight the nonlocal nature of the closure which allows for heat to flow against local temperature gradients. © 2001 American Institute of Physics.
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  • 3
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 230 (1971), S. 450-451 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] We have found 108mAg in biota and sediments collected at previous nuclear testing sites in the Pacific. We first detected the radionuclide in a composite sample of the hepatopancreases of spiny lobsters collected at Bikini Atoll in 1969, and have since measured its concentration in several samples ...
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  • 4
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 76 (1972), S. 1775-1783 
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Journal of Magnetism and Magnetic Materials 120 (1993), S. 48-52 
    ISSN: 0304-8853
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Journal of Magnetism and Magnetic Materials 120 (1993), S. 53-57 
    ISSN: 0304-8853
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 75 (1989), S. 223-234 
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Spatial defects in single crystals were imaged with ballistic phonons by their shadow projections using low-temperature scanning electron microscopy. Digital image recording and processing was applied for a quantitative evaluation of the experimental results. We have investigated sapphire and α-quartz samples with laser-drilled holes as special model cases of crystal defects. Computer algorithms have been developed to separate the shadows of the defects from the focusing pattern in the phonon images. We obtained binary images of the structures with a typical resolution of about 20 μm. Cross-correlation functions of two images were found to be well suited for image alignment procedures. By this technique and from theoretically calculated phonon intensity distributions the bolometer positions within the experimental phonon images could be determined automatically. Using two phonon detectors at different locations stereoscopical imaging of the defects became possible. From the different views the three-dimensional distribution of the defects could be calculated.
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 77 (1989), S. 79-89 
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We report experimental observations of the phonon focusing pattern in [100] GaAs using low temperature electron beam scanning for phonon generation. The typical dispersive effects for high-frequency phonons expected from the calculations by Tamura have clearly been observed using PbIn tunnel junctions for phonon detection. The quantitative comparison of our experimental results with the frequency dependent calculations by Tamura allowed to determine the dominant phonon frequencies contributing to the detector signal in our different experiments. Above the temperature of the λ-point the dominant phonon frequencies appear to be shifted considerably to lower values, which could be explained by a heating effect in the liquid-He layer adjacent to the tunnel junction detector. By comparing the observed magnitude of the detector signal with different theoretical treatments of the detector response, we have found satisfactory agreement for a model where the perturbation due to the high-frequency phonons is restricted to the base electrode of the detector reached first by the phonons following their passage through the crystal.
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 69 (1987), S. 69-76 
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Ballistic phonon propagation in single crystals has been used for imaging defect structures in bulk material. We have realized this principle by means of low-temperature scanning electron microscopy. As model cases we have imaged laser drilled holes in single-crystalline sapphire and α-quartz samples. Comparing the acoustic images with those obtained by optical transmission microscopy, we found that fine structure seen optically was well reproduced acoustically. In addition strain fields due to plastic deformations could clearly be imaged acoustically. The spatial resolution of our imaging technique is estimated to be a few micrometer. By using two or more phonon detectors, three-dimensional imaging of spatial inhomogeneities becomes possible.
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 75 (1989), S. 17-29 
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Ballistic phonon propagation in single-crystalline [001]-oriented gallium arsenide has been studied using low-temperature scanning electron microscopy for imaging. Deviations in the phonon focusing pattern due to dispersion effects were found by comparing the phonon images to theoretical calculations of the long-wavelength limit. The phonon propagation behavior in, samples cut from differently prepared wafers has been investigated. For highly impure crystals we found a pronounced increase of the diffusive signal component at the expense of the ballistic one. Samples with varying dislocation densities also showed a sensitive dependence, of the ballistic phonon propagation on these crystal defects. For focusing calculations considering elastic scattering processes the diffusivity of the phonons could be determined as a function of the mean scattering length. We have found phonon mean free paths of 0.35 mm to 0.80 mm for the various GaAs crystals.
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