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  • 1
    Electronic Resource
    Electronic Resource
    Improved instrument for medium energy electron diffraction and microscopy of surfaces (1985)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 56 (1985), S. 1215-1219 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The REMEDIE system for reflection electron microscopy and electron diffraction at intermediate energies (0.5–20 keV) has been rebuilt with an improved imaging resolution of better than 10 nm, a convenient and versatile system for observation diffraction patterns and provision for specimen preparation and treatment suitable for surface structural studies. The current capabilities of the instrument are illustrated by results obtained from cleaved and annealed silicon (111) surfaces with or without thin deposited silver and gold layers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1137978
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  • 2
    Electronic Resource
    Electronic Resource
    Lattice dynamics of a pair-potential model of α-quartz (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 8357-8361 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A pair potential for SiO2 proposed by Tsuneyuki, Tsukada, Aoki, and Matsui [Phys. Rev. Lett. 61, 869 (1988)] is used to calculate a range of lattice dynamical properties of α-quartz. The potential energy of the structure is minimized, and the phonon frequencies are calculated for the structural parameters corresponding to the energy minimum. Frequencies calculated throughout the Brillouin zone are used to construct a frequency distribution function and the harmonic contributions to the thermodynamic functions are calculated. The coefficients of thermal expansion perpendicular and parallel to the c axis are calculated in a perturbative approximation. The expansion coefficient parallel to the c axis is found to be negative at low temperatures, in agreement with experiment. The elastic, dielectric, and piezoelectric constants are also calculated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.461262
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  • 3
    Electronic Resource
    Electronic Resource
    Poloidal rotation effects on a simulated resistive kink mode (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 174-179 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Through the principal use of the reduced magnetohydrodynamic version of the finite aspect ratio code [L. A. Charlton et al., J. Comput. Phys. 86, 270 (1990)], an m/n=1/1 resistive kink mode was poloidally rotated with the accompanying rotational shear. It was observed that the growth rate of this unstable mode can either decrease or increase as the applied equilibrium rotation is increased to near poloidal sonic speeds. Shear in the poloidal rotation profile is stabilizing, but only if the destabilizing effects of bulk rotation can be overcome. Therefore, the mode's stability was sensitive to the location of the rotation's peak relative to the eigenmode's spatial extent. The destabilizing effects of bulk rotation are apparently a rotationally enhanced beta, and the stabilizing effects appear to be caused by exceeding a critical rotational shear spatially averaged over the eigenmode structure. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1326062
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  • 4
    Electronic Resource
    Electronic Resource
    Theory of beat wave excitation in an inhomogeneous plasma (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 36-47 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The theory of beat wave excitation in a slightly inhomogeneous plasma is presented. While the theory is general it applies directly to the experiments performed in Alaska by the ionospheric heating facilities HIPAS [High Power Auroral Simulation, Radio Sci. 25, 1269 (1990)] and HAARP [High Frequency Active Auroral Research Project, Geophys. Res. Lett. 25, 257 (1998)]. A ray tracing (WKB) formalism appropriate for computations is developed. The computational implementation of this formalism and extensive results will be presented in a follow up to this paper. Also the beat wave excitation of upper-hybrid waves is investigated analytically. The complicated trajectories of these waves in the plasma are described. When this beat wave reaches the plasma wave resonance it can, in the HIPAS–HAARP experiments, attain nonlinear amplitude. The electrostatic upper-hybrid waves are trapped around the density maximum of the ionosphere. This trapping is investigated in detail. Beat wave pumping of the trapped modes is possible using HAARP and HIPAS or with split beams from HAARP. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1329149
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  • 5
    Electronic Resource
    Electronic Resource
    Determination of the local Al concentration in AlxGa1−xAs-GaAs quantum well structures using the (200) diffraction intensity obtained with a 10 A(ring) electron beam (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 54 (1989), S. 1454-1456 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A novel method for determining the local concentration of Al in the AlxGa1−xAs layer of AlxGa1−xAs-GaAs multiple quantum well structures is reported. By scanning a 10 A(ring) electron beam across the interface, the (200) dark-field scanning transmission electron microscopy (STEM) image shows the contrast of the AlxGa1−xAs-GaAs multilayer since the intensity of the (200) diffraction is sensitive to the Al concentration. The line scan intensity profile of the (200) diffraction, along a uniform specimen region of known thickness, shows the intensity variation of the (200) diffraction and reflects the local content of Al in each region. The simulation of the nanodiffraction patterns produces a chart of the (200) diffraction intensity versus the Al concentration for the determination of the local change of the Al concentration. A molecular beam epitaxy grown AlxGa1−xAs-GaAs specimen (x=0.57 as determined from Raman spectroscopy) is tested and the dark-field STEM studies show two thin layers of x=0.46 at the 1/3 and 2/3 height level within every AlxGa1−xAs layer.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.100695
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  • 6
    Electronic Resource
    Electronic Resource
    Absolute magnetometry at nanometer transverse spatial resolution: Holography of thin cobalt films in a scanning transmission electron microscope (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 7418-7424 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A method for the absolute measurement of magnetization at nanometer spatial resolution in magnetic thin films has been developed. A biprism placed in the illumination system of a scanning transmission electron microscope allows the operation of two distinct holography modes. The absolute mode displays a linear change in phase difference for regions of constant magnetization and thickness and the slope determines the magnitude of magnetization. The differential mode displays a constant value of phase difference in these regions allowing a simple and straightforward determination of domain wall profiles. Micromagnetic structure extracted from identical areas of thin Co films is compared using the new holography modes, differential phase constrast Lorentz microscopy and conventional Fresnel Lorentz microscopy in the same instrument.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.356658
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  • 7
    Electronic Resource
    Electronic Resource
    Magnetic structures and interactions in Ho/Y, Ho/Lu, and Ho/Er superlattices (invited) : The 6th joint magnetism and magnetic materials (MMM)-intermag conference (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 6274-6277 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Ho/Y and Ho/Er superlattices have been grown by molecular-beam epitaxy using a Balzers UMS 630 instrument. The superlattices were grown on a sapphire substrate with an Nb buffer and Y seed layer. X-ray-diffraction techniques were used to characterize the crystallographic structure and neutron-diffraction techniques to determine the magnetic structures. The results for the Ho/Y systems were consistent with long-range order being formed coherently through the whole superlattice. The moments in the Ho layers were aligned in the basal plane and most of the structures could be described by helical structures with a turn angle between holmium planes of ΨH and between nonmagnetic Y planes ΨY. ΨY is found to be largely independent of temperature or superlattice, while ΨH decreases with decreasing temperatures and at low temperatures takes a commensurate value, so as to take advantage of the basal plane anisotropy. The results for the Ho/Er superlattices differ because the Er has a magnetic moment and the anisotropy favors alignment along the c axis. Between the ordering temperature of bulk Ho and bulk Er, the results are similar to those of the Ho/Y superlattices. The ordering propagates through the Er layers but the Er moments are not ordered. At lower temperatures the Er moments order in a cycloidal (a/c) structure with the basal plane components having fairly long-range coherence with the Ho moments, but the c-axis components having no coherence from one Er layer to the next.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.358303
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  • 8
    Electronic Resource
    Electronic Resource
    Detonation: A mechanism for the explosive release of energy in a plasma (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 1848-1852 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The explosive release of energy by a plasma is a common and striking occurrence. A novel explosive scenario is demonstrated in a simple system that becomes unstable to a line tied Rayleigh–Taylor–Parker instability. The system crosses the linear instability threshold in a narrow region. Initially the instability grows in the narrow region. Two nonlinear terms become important at low amplitude. One nonlinearity causes the mode to grow explosively and narrow into finger-like structures. The other nonlinearity broadens the mode into the linearly stable region. The explosive nonlinearity makes the linearly stable region metastable. The combination of the two nonlinearities causes the mode to progressively destabilize the metastable region. Since this process is reminiscent of the detonation of chemical explosives, it is called detonation. Without dissipation the kinetic energy released is proportional to (t0−t)−6.4. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871980
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  • 9
    Electronic Resource
    Electronic Resource
    Field-aligned coordinates for nonlinear simulations of tokamak turbulence (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 2687-2700 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Turbulence in tokamaks is characterized by long parallel wavelengths and short perpendicular wavelengths. A coordinate system for nonlinear fluid, gyrokinetic "Vlasov,'' or particle simulations is presented that exploits the elongated nature of the turbulence by resolving the minimum necessary simulation volume: a long thin twisting flux tube. It is very similar to the ballooning representation, although periodicity constraints can be incorporated in a manner that allows E×B nonlinearities to be evaluated efficiently with fast Fourier transforms (FFT's). If the parallel correlation length is very long, however, enforcing periodicity can introduce artificial correlations, so periodicity should not necessarily be enforced in the poloidal angle at θ=±π. This method is applied to high resolution three-dimensional simulations of toroidal ion temperature gradient (ITG) driven turbulence, which predict fluctuation spectra and ion heat transport similar to experimental measurements. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871232
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  • 10
    Electronic Resource
    Electronic Resource
    Nonlinear magnetohydrodynamic detonation: Part I (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 3565-3580 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The sudden release of magnetic free energy, as occurs in spectacular solar flare events, tokamak disruptions, and enigmatic magnetospheric substorms, has long defied any acceptable theoretical explanation. Usual attempts at explaining these explosive events invoke magnetic reconnection and/or ideal magnetohydrodynamic (MHD) instability. However, neither of these two mechanisms can explain the fast time scales without nonlinear destabilization. Recently, Cowley et al. [Phys. Plasmas 3, 1848 (1996)] have demonstrated a new mechanism for nonlinear explosive MHD destabilization of a line tied Rayleigh–Taylor model. In this paper, this picture is generalized to arbitrary magnetic field geometries. As an intermediate step, the ballooning equation in a general equilibrium is derived including the effects of magnetic field curvature, shear, and gravity. This equation determines the linear stability of the plasma configuration and the behavior of the plasma displacement along the magnetic field line. The nonlinear equation which determines the time and spatial dependence, transverse to the equilibrium magnetic field, of the plasma displacement is obtained in fifth order of the expansion. The equations show that explosive behavior is a natural and generic property of ballooning instabilities close to the linear stability boundary. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872252
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