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  • 1
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 1502-1511 
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The dependence on induced charge, experimental geometry, and temperature of electrostatic modes in very low aspect ratio non-neutral plasmas in a Penning trap is considered. The modes are of interest as non-destructive diagnostics of the shape of the plasmas. These investigations include equilibrium calculations of plasma shapes and profiles at finite temperature and particle-in-cell simulations of axisymmetric modes. The results of the simulations are compared to the zero-temperature theory by Dubin [Phys. Rev. Lett. 66, 2076 (1991)] taken to first-order in the aspect ratio and to experimental measurements by Weimer et al. [Phys. Rev. A 49, 3842 (1994)]. In general, it is concluded that the Dubin theory provides a means to obtain reasonable estimates of plasma parameters, including density, radius, and axial length, for plasmas in the very important regime for which the axial length is comparable to the Debye length. In addition, dependence on induced charge, equilibrium shape, and plasma temperature are identified which can likely be used to improve agreement between theory and experiment. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Pacing and clinical electrophysiology 22 (1999), S. 0 
    ISSN: 1540-8159
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Medizin
    Notizen: Mehra et al. (PACE 1980; 3:526) observed that immediately after implantation of a pacing electrode in a dog heart, the anodal refractory period (RP) is shorter than the cathodal RP, but after several weeks the anodal RP becomes longer than the cathodal RP. We examine this experiment using numerical simulations based on the bidomain model of cardiac tissue and a Beeler-Reuter membrane. Our hypothesis is that accumulation of inexcitable tissue around the electrode following implantation causes the effective size of the electrode to increase and that this increase is the mechanism underlying the change in RP. We calculate that the anodal RP is shorter than the cathodal RP for both large and small electrodes. However, for large electrodes the threshold for anode “break” stimulation is greater than 8 mA. Mehra et al. defined RP experimentally as the interval at which the threshold stimulus strength becomes greater than 8 mA. If we restrict the stimulus current in our calculations to less than 8 mA, we exclude anode break stimulation from our calculation of the RP. In that case, our results are consistent with Mehra et al. and suggest that their observation resulted from their definition of RP.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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