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  • 1990-1994  (5)
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  • 1
    Electronic Resource
    Electronic Resource
    A flow reactor system for catalytic reaction studies, allowing time- and space-resolved measurements of gas composition and temperature around the catalyst (1994)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 65 (1994), S. 2696-2703 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A flow reactor system for catalytic reaction studies is described. The system is equipped with a movable gas sampling device and on-line mass spectrometry (MS), allowing time- and space-resolved measurements of gas composition and temperature. Results from H2 oxidation on Pt are used to illustrate the system performance. Spatial variations of H2, O2, and H2O concentrations can be measured, e.g., during mass transport limited conditions. Temporal variations in H2, O2, and H2O during chemical oscillations are well resolved close to the catalyst, but successively smeared away at increasing distance. The special design of the gas sampling probe allows quantible MS measurement even of H2O and other "difficult'' gases, and of gas temperature variations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1144672
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Andreev-reflection in YBCO “break-junctions” (1992)
    Springer
    The European physical journal 87 (1992), S. 275-279 
    Details
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We present measurements at break-junctions prepared of polycrystalline and textured YBCO-pellets with different resistances. The higher-ohmic junctions show the well known behaviour of HTSC-tunnel contacts with gap-like structures in their dI/dV-characteristics. Lower-ohmic junctions show the behaviour of point contacts. TheirI(VV)-and dI/dV-characteristics indicate all properties of the Andreev-reflection corresponding to the theory of Kümmel et al. [1] for BCS-superconductors. This could be an alternative method to study the energy gap in high temperature superconductors. Additionally we will show, that sharp minima in the dI/dV-characteristics could also be explained by the process of Andreev-reflection. For correcting the measured characteristics we substract the typical background to compare the characteristics directly with theoretical calculations. We studied the influence of magnetic fields up to 8 T.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01309280
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Measurements of the dynamic conductance on SS-and NS-point contacts (1994)
    Springer
    The European physical journal 94 (1994), S. 21-28 
    Details
    ISSN: 1434-6036
    Keywords: 74.50
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Mechanically point contacts made of Ta, Al, Ag (anvil) and of Ta, Ag (needle) were investigated in the temperature range between 4.2 K and 1.3 K and in magnetic fields up to 0.8 T. For point contacts consisting of two superconducting electrodes we measured the current voltage characteristics and also the dynamic conductance. The characteristics with a negative differential conductance and the occurrence of an excess current point to the appearance of Andreev-multiple reflection at an SNS-interface in the contact region. The investigated current voltage characteristics and the dynamic conductance of typical NS-point contacts (Ta−Ag and Ta−Al) point to a microconstriction with a barrier of arbitrary strength at the interface between the normalconductor and the superconductor. We performed theoretical calculations forT=0 and also for temperatures up to the critical temperature using the model of Blonder, Tinkham and Klapwijk (BTK model). In this model the Andreev-reflection is the main scattering mechanism at the NS-interface but also elastic scattering and transmission processes are taken into consideration. The comparison of our theoretical results with the experimental results and also the determined excess current at all investigated point contacts lead to the assumption that there exist metallic contacts with very small barrier strengths at the NS-interface where the Andreev-reflection is the dominant process and the other scattering mechanisms play a subdominant role.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01307650
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Andreev-reflection in highly doped Pb/n−InSb/Pb junctions (1993)
    Springer
    The European physical journal 92 (1993), S. 187-190 
    Details
    ISSN: 1434-6036
    Keywords: 74.50
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We studied the carrier transport through n-InSb-films sandwiched between two superconducting lead electrodes. These n-InSb-films were about 30 nm thick, polycrystalline and very highly doped (1021 cm−3). TheV(I)- and dV/dI (V)-characteristics indicated all the properties of Andreev-reflection (subharmonic energygap structures (SGS) and excess current) according to the theory of Octavio et al. (OTBK-model) [1, 2]. Our measurements show the temperature dependence of these structures and also the influence of magnetic fields up to 80 mT and give a further reference to the importance of Andreev-reflection in semiconductor-coupled superconducting junctions (SSmS junctions).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01312175
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    Paper (German National Licenses)
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  • 5
    Electronic Resource
    Electronic Resource
    Andreev-reflection in semiconductor-coupled superconducting weak-links (1994)
    Springer
    The European physical journal 96 (1994), S. 13-24 
    Details
    ISSN: 1434-6036
    Keywords: 74.50
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We investigated the carrier transport through highly dopedn—InSb-films sandwiched between two superconducting lead electrodes. The measuredI(V)- anddV/dI(V)-characteristics show a very clear subharmonic gap structure (SGS) and an excess current, indicating the occurrence of multiple Andreev-reflection between the two semiconductor-superconductor interfaces. For the theoretical background we consult the theory of Octavio et al. (OTBK-model). We show that the application of this theory leads to some difficulties. According to this we propose some modifications, which in our opinion give a better description of the real situation in such contacts. We calculated theI(V)- anddV/dI(V)-characteristics of junctions with dissimilar barrier strength at the two interfaces as well as such for different superconductors, and compare these results with the experimental observations. We studied the influence of electromagnetic radiation on the junctions properties experimentally as well as theoretically for frequencies ranging in the classical limit. Moreover we evaluate the temperature dependence of the excess current, compare it with theoretical results and give an estimation of the barrier strength. The critical current is studied in dependence on the temperature and in comparison with calculations of Kuprianov and Lukichev (KL-theory), as well as under rf-application.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01313010
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    Paper (German National Licenses)
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