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  • 1
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 46 (1986), S. 0 
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: The regional distributions of thyrotrophin-releasing hormone (TRH) and substance P in postmortem human spinal cord were determined by radioimmunoassay in fresh tissue taken from 22 patients who died without known neurological disease. Dorsal, ventral, and intermediolateral spinal cord regions were obtained from different segmental levels (lumbar L1, 2, 3, and 4; thoracic groups T1–3, T4–6, T7–9, and T10–12) together with selective regions of grey matter of lumbar spinal cord. The effects on peptide levels of (a) the age of the patient, (b) the postmortem time interval, and (c) freezing the tissue samples prior to assay were assessed. Levels of 5-hydroxytryptamine (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) were determined in regional lumbar and thoracic tissue using HPLC with electrochemical detection. Substance P was found in the highest concentration in the dorsal spinal cord, with no significant segmental differences. In contrast, TRH was present in higher levels in the ventral rather than the dorsal spinal cord, with segmental differences. There was a significant difference in the 5-HT/5-HIAA ratio between dorsal and ventral spinal cord, with the highest ratio in the ventral spinal cord. There were no significant differences in substance P, TRH, or 5-HT levels in spinal cords between 5 and 20 h postmortem or from patients aged between 65 and 90 years. Freezing the tissue (– 80°C for 24 h) prior to assay significantly reduced TRH and substance P levels compared to samples assayed immediately without prior freezing. The levels and distribution of peptides and indoleamines in human spinal cord are compared with those previously reported in the rat and other species and the possible roles of these substances in the control of motor function and autonomic control are discussed.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 1 (1989), S. 545-554 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Particle orbits in a rotating tokamak plasma are calculated from the equation of motion in the frame that rotates with the plasma. It is found that heavy particles in a rotating plasma can drift away from magnetic surfaces significantly faster with a higher bounce frequency, resulting in a diffusion coefficient much larger than that for a stationary plasma. Particle orbits near the surface of a rotating tokamak are also analyzed. Orbit effects indicate that more impurities can penetrate into a plasma rotating with counterbeam injection. Particle simulation is carried out with realistic experimental parameters and the results are in qualitative agreement with some experimental observations in the Tokamak Fusion Test Reactor (TFTR) [in Proceedings of the 14th European Conference on Controlled Fusion and Plasma Heating (European Physical Society, Brussels, 1987), p. 121].
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 31 (1988), S. 2030-2036 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Direct excitation and propagation of ion Bernstein waves from low-impedance current-carrying loop antennas in the ion cyclotron frequency range are studied over a range of plasma and antenna parameters. The dependence of wave coupling efficiency on plasma density and on wave frequency and parallel wavelength is obtained from measurements of wave amplitude and variations in antenna impedance. Comparisons are made to a simple nonuniform warm-plasma model of the coupling problem. Generally good agreement is found between theory and experiment. As a result, some guidelines are proposed concerning antenna design.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 30 (1987), S. 834-839 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Current generation by asymmetrical heating of minority ions without the injection of net momentum into a plasma is studied numerically by solving the Fokker–Planck equation in which the quasilinear diffusion term for cyclotron absorption is added to the Coulomb collision terms. The results show that current drive efficiency is better in a H–D plasma than in a 3He–D plasma. The applicability of asymmetrical minority ion heating current drive in a hydrogen tokamak plasma with the existence of impurity ions is also investigated. The practicality of this current drive process for fusion reactors is discussed.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 28 (1985), S. 716-733 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Lower-hybrid waves are studied in the Princeton ACT-I steady-state toroidal plasma device using a radially scanning CO2 laser scattering system with both amplitude and phase sensitive detection techniques. Clearly defined resonance cones launched from external electrostatic antennas are seen to disappear as the plasma density is raised. Scaling of a lower-hybrid wave (LHW) laser signal with radio-frequency (rf) power in the presence of resonance cones shows nonlinearities associated with rf-induced changes in the effective laser scattering volume. Absolute fluctuation level estimates suggest that this occurs when eΦ/Te≥1. Wave-front curvature effects can cause a complete loss of resonance cone laser signals, even though probes indicate that cones are still present. Measurements of the wave k⊥ spectrum in the plasma show direct evidence for electron Landau filtering of the original wave k(parallel) spectrum launched from the antenna at the plasma edge, and strong dependence on antenna phasing. Finally, frequency shifts and loss of the resonance cone signal are associated with high levels of plasma density edge turbulence.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 28 (1985), S. 2453-2457 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Parasitic excitation of ion Bernstein waves is observed from a Faraday-shielded fast wave loop antenna in the ion-cyclotron frequency range. Local analysis of the Vlasov–Maxwell equations demonstrates the role of the plasma density gradient in the coupling process. The effects of plasma density and of parallel wavenumber on the excitation process are investigated.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 28 (1985), S. 2845-2847 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The backward branch of the electrostatic ion-cyclotron wave has been observed for the first time. The wave, which was driven by a phased antenna structure inserted in a neon plasma, exists in the parameter ranges 2Ti/mi(very-much-less-than)(ω/k(parallel))2(very-much-less-than)2Te/me, nΩi〈ω〈(n+1)Ωi, Te(approximately-greater-than)Ti, and ωpi〉Ωi. Double-tip probe interferometry data agree with the theoretical dispersion relation. The antenna couples into the wave more readily on the side of the antenna where it has its smallest wavenumber.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 28 (1985), S. 3365-3379 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: One- and two-dimensional particle simulations of beam–plasma interaction have been carried out in order to understand current drive experiments that use an electron beam injected into the Advanced Concepts Torus (ACT)-1 device [Rev. Sci. Instrum. 53, 409 (1982)]. Typically, the initial beam velocity along the magnetic field is V0=109 cm/sec, while the thermal velocity of the background electrons is vt=108 cm/sec. The ratio of the beam density to the background density is about 10% so a strong beam–plasma instability develops, causing rapid diffusion of beam particles. For both one- and two-dimensional simulations, it is found that a significant amount of beam and background electrons are accelerated considerably beyond the initial beam velocity when the beam density is more than a few percent of the background plasma density. In addition, the electron distribution along the magnetic field has a smooth negative slope, f'(v(parallel))〈0, for v(parallel)〉0 extending to v(parallel)=1.5 V0∼2 V0, which is in sharp contrast to the predictions from quasilinear theory. An estimate of the mean-free path for beam electrons caused by Coulomb collisions reveals that the beam electrons can propagate a much longer distance than is predicted from a quasilinear theory because of the presence of a high-energy tail. These simulation results agree well with the experimental observations from the ACT-1 device.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 59 (1988), S. 2084-2086 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We present a probe arrangement for electrostatic wave measurements in plasmas. The probe picks up potential perturbation by capacitive coupling to a copper sensor. It has the advantages of high resolution (within 5 mm) and easy construction.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 60 (1986), S. 4322-4324 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The first experimental observation of current generation by asymmetrical heating of ions is reported. Ions were asymmetrically heated by a unidirectional fast Alfvén wave launched by a slow wave antenna inside a tokamak. Current generation was detected by measuring the asymmetry of the toroidal plasma current with probes at the top and bottom of the toroidal plasma column.
    Type of Medium: Electronic Resource
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