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  • American Institute of Physics (AIP)  (55)
  • Cambridge University Press  (24)
  • 1995-1999  (74)
  • 1915-1919  (5)
  • 1
    Digitale Medien
    Digitale Medien
    X-ray photoemission and absorption spectroscopy of supported nanoscale iron clusters (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 2651-2654 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Fe particles with sizes in the range 1–5 nm, formed by a gas-aggregation method and deposited onto graphite and C60 supports, were studied by x-ray photoemission spectroscopy, x-ray absorption spectroscopy, and magnetic linear dichroism. Clusters deposited onto a C60 coated graphite substrate become embedded within the fullerene film, and have an increased resistance to oxidation compared to exposed clusters supported on a graphite surface. No evidence for hybridization between the electronic states of Fe and C60 is seen. The magnetic dichroism signal of the exposed clusters increases sharply with the film thickness because of the increased cluster interactions. © 1999 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.371105
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  • 2
    Digitale Medien
    Digitale Medien
    Experimental constraints on transport from dimensionless parameter scaling studies : The 39th annual meeting of division of plasma physics of APS (1998)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 5 (1998), S. 1695-1702 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The scalings of heat transport with safety factor (q), normalized collisionality (ν), plasma beta (β), and relative gyroradius (ρ*) have been measured on the DIII-D tokamak [Fusion Technol. 8, 441 (1985)]. The measured ρ*, β and ν scalings of heat transport indicate that E×B transport from drift wave turbulence is a plausible basis for anomalous transport. For high confinement (H) mode plasmas where the safety factor was varied at fixed magnetic shear, the effective (or one-fluid) thermal diffusivity was found to scale like χeff∝q2.3±0.64 , with the ion and electron fluids having the same q scaling to within the experimental errors except near the plasma edge. The scaling of the thermal confinement time with safety factor was in good agreement with this local transport dependence, τth∝q−2.42±0.31 ; however, when the magnetic shear was allowed to vary to keep q0 fixed during the (edge) safety factor scan, a weaker global dependence was observed, τth∝q95−1.43±0.23. This weaker dependence was mainly due to the change in the local value of q between the two types of scans. The combined ρ*, β , ν and q scalings of heat transport for H-mode plasmas on DIII-D reproduce the empirical confinement scaling using physical (dimensional) parameters with the exception of weaker power degradation. © 1998 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.872838
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  • 3
    Digitale Medien
    Digitale Medien
    The asymptotic motion of an accelerating, thick layer of inviscid liquid (1998)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 10 (1998), S. 101-112 
    Details
    ISSN: 1089-7666
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Most studies of a gravitationally unstable interface between a liquid and a gas by boundary integral techniques prescribe the motion of the liquid in the far field. The mean gas pressure at the interface is then irrelevant in its motion. On the other hand, when a pressure jump is applied to a liquid column in a vertical duct, its acceleration is determined by the pressure jump no matter how tall the column. Previous studies of accelerating liquid layers [G. R. Baker, R. L. McCrory, C. P. Verdon, and S. A. Orszag, "Rayleigh–Taylor instability of fluid layers," J. Fluid Mech. 178, 161 (1987)] show that the motion of the gravitationally unstable interface depends on the reciprocal of the mean layer thickness H. In this paper, we derive an asymptotic boundary integral method that captures the O(1/H) effects on the motion of the unstable interface with a correction that is exponentially small in H. The validity of the asymptotic approach is confirmed by comparison with numerical simulations of the liquid layer. The success of the approach relies on expansions of the kernels in the boundary integrals, indicating that the procedure for deriving the asymptotic equations is more general than just for vertical ducts or periodic geometry. In a subsequent paper, we use our approach to derive the equations for the formation of a bubble at a submerged orifice that is driven by an increase in gas pressure. © 1998 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.869553
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  • 4
    Digitale Medien
    Digitale Medien
    Density profile consistency and its relation to the transport of trapped versus passing electrons in tokamaks (1998)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 5 (1998), S. 2936-2941 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A formal expression for the canonical steady-state density profile in a tokamak can be obtained from the Fokker–Planck-type diffusion equation derived from the Vlasov equation in the limit of anomalous diffusion due to strong turbulence. Here we derive an explicit expression for this canonical profile for a tokamak with arbitrary cross section and aspect ratio. The resulting profile is independent of the spatial dependence of the diffusion coefficient, but does depend on the relative diffusion of trapped versus passing particles. Under conditions where only the trapped particles transport due to interactions with the turbulence the profiles are considerably flatter than if both the trapped and passing transport the same. The steepness of the calculated profile depends on the ratio of the diffusion coefficients for passing and trapped particles. The calculated profiles are compared with measured profiles from the tokamak known as DIII-D [J. L. Luxon et al., Plasma Physics and Controlled Nuclear Fusion Research 1986 (International Atomic Energy Agency, Vienna, 1987), Vol. I, p. 159]. Density profiles for a typical International Thermonuclear Experimental Reactor (ITER) [R. Aymar, Fusion Eng. Design 24, 977 (1984)] plasma are also derived. © 1998 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.873016
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  • 5
    Digitale Medien
    Digitale Medien
    Observation of the Langmuir decay instability driven by stimulated Raman scattering (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 3012-3020 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Thomson scattering was used to measure the Langmuir wave spectrum driven by stimulated Raman scattering. The Thomson scattering signals measured in the experiment showed Langmuir waves with components both parallel and antiparallel to the incident laser's wave vector, k0. The parallel component was attributed to stimulated Raman scattering. However, the Langmuir waves with components antiparallel to k0, which cannot be explained by stimulated Raman scattering, were attributed to the Langmuir decay instability (LDI). The relative amplitude of the two Langmuir wave features and their angular width supported the conclusion that the Langmuir waves traveling antiparallel to the incident laser's wave vector were driven by the Langmuir decay instability. © 1997 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.872436
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  • 6
    Digitale Medien
    Digitale Medien
    Meeting the challenge of detecting ion plasma waves (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 2207-2215 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Ion plasma waves—purely electrostatic ion waves with a wavelength of order of the electron Debye length and frequency of the order of the ion plasma frequency—have long been known in theory but have proven difficult to detect experimentally. The difficulties stemmed from the techniques used to produce the plasma and to drive and detect the waves. In the work reported here, these problems were overcome by using resonant laser scattering to detect ion plasma waves in a multiply ionized, laser-produced plasma. This nonetheless required careful experimental design to minimize frequency smearing of the scattered signal by plasma gradients. The plasma was extensively characterized, allowing comparison of the theoretical dispersion relation with the wave data. The agreement of these two provides conclusive proof of the detection of ion plasma waves. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.871243
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  • 7
    Digitale Medien
    Digitale Medien
    The role of symmetry in indirect-drive laser fusion (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 2488-2494 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Good radiation drive symmetry will be crucial for achieving ignition in laboratory inertial fusion experiments. The indirect-drive inertial confinement fusion (ICF) method utilizes the soft x-ray field in a radiation-containing cavity, or hohlraum, to help achieve a high degree of symmetry. Achievement of the conditions necessary for ignition and gain will require experimental fine tuning of the drive symmetry. In order to make tuning possible, a significant effort has been devoted to developing symmetry measurement techniques. These techniques have been applied to a series of experiments that give a graphic picture of the symmetry conditions in the complex hohlraum environment. These experiments have been compared with detailed, fully integrated theoretical modeling. The ultimate goal of this work is the detailed understanding of symmetry conditions and the methods for their control. Comparison with experiments provides crucial benchmarking for the modeling—a key element in planning for ignition. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.871210
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  • 8
    Digitale Medien
    Digitale Medien
    Inverting chaos: Extracting system parameters from experimental data (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Chaos 6 (1996), S. 528-533 
    Details
    ISSN: 1089-7682
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Given a set of experimental or numerical chaotic data and a set of model differential equations with several parameters, is it possible to determine the numerical values for these parameters using a least-squares approach, and thereby to test the model against the data? We explore this question (a) with simulated data from model equations for the Rossler, Lorenz, and pendulum attractors, and (b) with experimental data produced by a physical chaotic pendulum. For the systems considered in this paper, the least-squares approach provides values of model parameters that agree well with values obtained in other ways, even in the presence of modest amounts of added noise. For experimental data, the "fitted'' and experimental attractors are found to have the same correlation dimension and the same positive Lyapunov exponent. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.166200
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  • 9
    Digitale Medien
    Digitale Medien
    Density profile consistency, particle pinch, and cold pulse propagation in DIII-D (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 2229-2236 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: It has been recently proposed that, for highly turbulent discharges, there exists a consistent density profile for the trapped electrons in a high aspect ratio circular cross-section tokamak, which has a radial variation proportional to 1/q(r), where q is the usual safety factor. It is shown here that this result can be extended to include passing electrons and noncircular cross-section moderate aspect ratio tokamaks. This new prediction for the density profile is compared to the time evolution of the measured electron density profile in low confinement mode (L-mode) shots in the tokamak known as DIII-D [L. Luxon et al., Plasma Physics and Controlled Nuclear Fusion Research, 1986 (International Atomic Energy Agency, Vienna, 1987), Vol. I. p. 159], where the q profile is changed in time during the discharge. Once an expression for the consistent density profile is known, it is trivial to obtain an expression for Vp/D, where Vp is the particle pinch velocity and D is the particle diffusion coefficient. This expression is compared with the value of Vp/D, which is obtained from an analysis, utilizing the ONETWO transport code [R. Dominguez and R. Waltz, Nucl. Fusion 27, 65 (1987)], of certain high confinement mode (H-mode) DIII-D discharges, which are free from edge localized modes. The dependence of density on q can be extended to a dependence of temperature on q through the adiabatic relation. The dependence of temperature on q can then predict one type of cold pulse propagation phenomena. By way of introduction, a simple analogy with a dynamic incompressible fluid system is made.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.872386
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  • 10
    Digitale Medien
    Digitale Medien
    Critical issues in space plasma physics : The 40th annual meeting of the division of plasma physics of the american physical society (1999)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 6 (1999), S. 1700-1708 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: It has been shown that solar, magnetospheric, and ionospheric plasmas exhibit remarkable global coherence and collective behavior. On the small scale, it has been possible in space research to perform experiments in what has been characterized as a "laboratory without walls." Wave–particle interactions, particle acceleration, and transport phenomena have been studied in revealing detail. There remain many outstanding issues in space plasma research such as the location, timing, and detailed mechanisms of magnetic reconnection; the processes of rapid particle acceleration to relativistic energies; the physics of thin current sheets; and the nature of a host of plasma instabilities in ionospheric, magnetospheric, and solar contexts. In this paper we provide a guide to special jargon and concepts employed in space plasma research. An assessment is made of the present state of observational and theoretical investigations in critical areas and possible future directions in space plasma research are considered. © 1999 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.873428
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