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  • American Chemical Society  (48)
  • American Institute of Physics (AIP)  (14)
  • 1995-1999  (62)
  • 1965-1969
  • 1999  (62)
  • 1
    Electronic Resource
    Electronic Resource
    Moyal–Nahm equations (1999)
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 40 (1999), S. 2539-2548 
    Details
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: Various aspects of the Nahm equations in three and seven dimensions are investigated. The residues of the variables at simple poles in the seven-dimensional case form an algebra. A large class of matrix representations of this algebra is constructed. The large N limit of these equations is taken by replacing the commutators by Moyal brackets, and a set of nontrivial solutions in a generalized form of Wigner distribution functions is obtained. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.532713
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  • 2
    Electronic Resource
    Electronic Resource
    Obtaining absolute spatial flux measurements with a time-resolved pinhole camera (1999)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 70 (1999), S. 2012-2015 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A technique is described to determine the spatial x-ray flux emitted from a hohlraum wall and subsequently transmitted through a diagnostic hole. This technique uses x-ray diodes, bolometers, and a time-resolved pinhole camera to determine the spatial flux of x rays emitted through a hohlraum's diagnostic hole. The primary motivation for this analysis was the relatively long duration, nearly 100 ns, of the x-ray drive present in z-pinch driven hohlraums. This radiation causes plasma to ablate from the hohlraum walls surrounding the diagnostic hole and results in a partial obscuration that reduces the effective area over which diagnostics view the radiation. The effective change in area leads to an underestimation of the wall temperature when nonimaging diagnostics such as x-ray diodes and bolometers are used to determine power and later to infer a wall temperature. An analysis similar to the one described below is then necessary to understand the radiation environment present in x-ray driven hohlraums when these diagnostics are used and hole closure is important. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1149703
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  • 3
    Electronic Resource
    Electronic Resource
    X-ray spectral power measurements utilizing the diffraction pattern of a slit (1999)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 70 (1999), S. 1624-1626 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: An instrument is described which can obtain x-ray spectral power measurements utilizing the diffraction pattern produced when x rays pass through a slit. Traditionally, these types of measurements yielding low to moderate spectral resolution have been made with filtered x-ray diodes or with a transmission grating. The instrument described below has several advantages over filtered x-ray diodes in determining the spectral power profile such as an insensitivity to surface contamination. In addition, this instrument does not require the use of filters which can be destroyed during a shot making absolute measurements difficult and very time consuming. The advantages over a transmission grating system include cost, mechanical robustness, and fewer components which require spectral calibration. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1149642
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  • 4
    Electronic Resource
    Electronic Resource
    Polarization around an ion in a dielectric continuum with truncated electrostatic interactions (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 10679-10692 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In order to reduce computational effort and to allow for the use of periodic boundary conditions, electrostatic interactions in explicit solvent simulations of molecular systems do not obey Coulomb's law. Instead, a number of "effective potentials" have been proposed, including truncated Coulomb, shifted, switched, reaction-field corrected, or Ewald potentials. The present study compares the performance of these schemes in the context of ionic solvation. To this purpose, a generalized form of the Born continuum model for ion solvation is developed, where ion–solvent and solvent–solvent interactions are determined by these effective potentials instead of Coulomb's law. An integral equation is formulated for calculating the polarization around a spherical ion from which the solvation free energy can be extracted. Comparison of the polarizations and free energies calculated for specific effective potentials and the exact Born result permits an assessment of the accuracy of these different schemes. Additionally, the present formalism can be used to develop corrections to the ionic solvation free energies calculated by molecular simulations implementing such effective potentials. Finally, an arbitrary effective potential is optimized to reproduce the Born polarization. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479013
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  • 5
    Electronic Resource
    Electronic Resource
    Geometry optimization in delocalized internal coordinates: An efficient quadratically scaling algorithm for large molecules (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 4986-4991 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Using a Z-matrix-like approach for generating new Cartesian coordinates from a new geometry defined in terms of delocalized internal coordinates, we eliminate the costly O(N3) iterative back-transformation required in standard geometry optimizations using delocalized (or natural/redundant) internals, replacing it with a procedure which is only O(N). By replacing the gradient transformation with an iterative solution of a set of linear equations, we also reduce this step from O(N3) to roughly O(N2). This allows a very efficient method for geometry optimization of large molecules in internal coordinates. Several optimizations on systems containing up to 500 atoms are presented, comparing the performance of the new algorithm with its predecessor, and demonstrating the practical utility and efficiency of our approach. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.478397
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  • 6
    Electronic Resource
    Electronic Resource
    Measurement of the frequency and spectral width of the Langmuir wave spectrum driven by stimulated Raman scattering (1999)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 6 (1999), S. 4284-4292 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Thomson scattering was used to measure the spectrum of Langmuir waves, in both frequency and wave number, driven below quarter-critical density by a laser beam. These measurements were capable of detecting and identifying waves driven by stimulated Raman scattering (SRS) and also of detecting waves driven by other effects such as the bump-on-tail instability postulated by the enhanced Thomson scattering model of Raman emission. The observed Langmuir waves were consistent with SRS and not with other possible sources. The width in k-space of the measured Thomson scattering signals also has implications for the saturation amplitude of the Langmuir waves. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873706
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  • 7
    Electronic Resource
    Electronic Resource
    Electron heat transport in improved confinement discharges in DIII-D : 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. 1978-1984 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In DIII-D [J. L. Luxon and L. G. Davis, Fusion Technol. 8, 441 (1985)] tokamak plasmas with an internal transport barrier (ITB), the comparison of gyrokinetic linear stability (GKS) predictions with experiments in both low and strong negative magnetic shear plasmas provide improved understanding for electron thermal transport within the plasma. Within a limited region just inside the ITB, the electron temperature gradient (ETG) modes appear to control the electron temperature gradient and, consequently, the electron thermal transport. The increase in the electron temperaturegradient with more strongly negative magnetic shear is consistent with the increase in the ETG mode marginal gradient. Closer to the magnetic axis the Te profile flattens and the ETG modes are predicted to be stable. With additional core electron heating, FIR scattering measurements near the axis show the presence of high k fluctuations (12 cm−1), rotating in the electron diamagnetic drift direction. This turbulence could impact electron transport and possibly also ion transport. Thermal diffusivities for electrons, and to a lesser degree ions, increase. The ETG mode can exist at this wave number, but it is computed to be robustly stable near the axis. Consequently, in the plasmas we have examined, calculations of drift wave linear stability do not explain the observed transport near the axis in plasmas with or without additional electron heating, and there are probably other processes controling transport in this region. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873494
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  • 8
    Electronic Resource
    Electronic Resource
    Collective phenomena in the inner magnetosphere (1999)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 6 (1999), S. 4195-4199 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The Earth's magnetosphere exhibits substantial complexity in many of its physical properties. Particle populations wax and wane and magnetic fields fluctuate on virtually all observed time scales, from less than 1 minute to many days. Much of the variability of the magnetosphere and its interaction with the ionosphere can be ascribed to the phenomena termed "substorms" and "storms." Ample evidence is found that these geospace disturbances, though exhibiting event-to-event differences, are remarkably repetitive and have basic underlying similarities. The ring current development, radiation belt particle changes, and basic substorm patterns suggest a high degree of coherence in the phenomena. Observations, modeling, and basic physical properties are discussed here that point to a relatively ordered, low-dimensional underlying dynamics in the magnetosphere. These results suggest that nonlinear processes and couplings introduce much of the observed complexity in magnetospheric particle and field changes. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873685
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  • 9
    Electronic Resource
    Electronic Resource
    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
    Source: AIP Digital Archive
    Topics: Physics
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873428
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  • 10
    Electronic Resource
    Electronic Resource
    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
    Source: AIP Digital Archive
    Topics: Physics
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.371105
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