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  • Articles  (119)
  • American Physical Society  (107)
  • American Institute of Physics (AIP)  (12)
  • 1995-1999  (101)
  • 1970-1974  (18)
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  • Articles  (119)
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  • 1
    Electronic Resource
    Electronic Resource
    Quasi-two-dimensional fast kinematic dynamo instabilities of chaotic fluid flows (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 2564-2578 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: This paper tests previous heuristically derived general theoretical results for the fast kinematic dynamo instability of a smooth, chaotic flow by comparison of the theoretical results with numerical computations on a particular class of model flows. The class of chaotic flows studied allows very efficient high resolution computation. It is shown that an initial spatially uniform magnetic field undergoes two phases of growth, one before and one after the diffusion scale has been reached. Fast dynamo action is obtained for large magnetic Reynolds number Rm. The initial exponential growth rate of moments of the magnetic field, the long time dynamo growth rate, and multifractal dimension spectra of the magnetic fields are calculated from theory using the numerically determined finite time Lyapunov exponent probability distribution of the flow and the cancellation exponent. All these results are numerically tested by generating a quasi-two-dimensional dynamo at magnetic Reynolds number Rm of order up to 105. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871964
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  • 2
    Electronic Resource
    Electronic Resource
    Chaotic flows and kinematic magnetic dynamos: A tutorial review : 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. 1636-1646 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: This paper reviews results on fast kinematic dynamo theory, emphasizing the recent realization that Lagrangian chaos of the underlying flow is the key element for understanding of the problem. Simple models for singular behavior of the magnetic field in the large magnetic Reynolds number limit are described and used to illustrate the tendency for fractal magnetic field distributions with extreme cancellation properties. The relation of ergodic properties of the chaotic flow to properties of the dynamo (e.g., growth rate, fractal dimension) are also discussed. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872832
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  • 3
    Electronic Resource
    Electronic Resource
    Scaling properties of magnetic dynamo wavenumber power spectra generated by Lagrangian chaotic flows (1998)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 5 (1998), S. 151-155 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Wavenumber power spectra of the magnetic field in kinematic dynamos of Lagrangian chaotic flows are investigated. Numerical integration of the kinematic dynamo equations with magnetic Reynolds number Rm up to 105 shows that the wavenumber power spectrum of the magnetic field generated by smooth, Lagrangian chaotic flows obeys a power-law. This property is theoretically predicted by a wavepacket model, whereby magnetic field wavepackets are evolved according to ordinary differential equations. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872713
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  • 4
    Electronic Resource
    Electronic Resource
    Targeting in Hamiltonian systems that have mixed regular/chaotic phase spaces (1997)
    Woodbury, NY : American Institute of Physics (AIP)
    Chaos 7 (1997), S. 512-519 
    Details
    ISSN: 1089-7682
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The problem of directing a trajectory of a chaotic dynamical system to a target has been previously considered, and it has been shown that chaos allows targeting using only small controls. In this paper we consider targeting in a Hamiltonian system, whose phase space contains a mixture of regular quasi-periodic and chaotic regions. A multistep forward–backward method targeting strategic intermediate points is found to be efficient and robust. It takes full advantage of the phase space structure and is believed to yield optimal transport times. It is robust under the influence of small noise and small modeling errors and recovers from temporary loss of control. Two illustrative examples, the standard map and the restricted circular three body problem, are presented. (The latter corresponds to motion of a space probe in the presence of the earth and the moon.) Comparisons are made of our method to other targeting strategies. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.166277
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  • 5
    Electronic Resource
    Electronic Resource
    Current-biased superconducting strips as position-sensitive particle detectors (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 2231-2243 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The feasibility of superconducting strips as position-sensitive detectors for α particles was investigated. For this purpose films have been prepared of different materials and dimensions using standard evaporation and laser ablation in an UHV system. Films were patterned into strips and current-biased strips were irradiated with 5.5 MeV α particles. The energy deposited by the particle in the strip creates a normal-conducting region, which in turn causes a voltage drop. The time evolution of the voltage drop across the strip as a function of bath temperature and bias current has been investigated. Information about the site of the strip hit by the α particle was obtained from monitoring the propagating normal-conducting zones. A lateral position sensitivity of ±30 μm for a tantalum strip detector has been achieved. The propagation of normal-state zones in the strip cannot provide information on the energy of the particle. A model describing the time evolution of a normal-conducting zone in a current-biased superconducting strip was used to test and interpret the experimental results and allows one to estimate the thermal conductivity of the strip material and the heat transfer from the strip into the substrate. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.358810
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  • 6
    Electronic Resource
    Electronic Resource
    Structural and tribological characterization of protective amorphous diamond-like carbon and amorphous CNx overcoats for next generation hard disks (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 3142-3154 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Further insight into processing-structure-property relationships have been carried out for existing and candidate carbon-based protective overcoats used in the magnetic recording industry. Specifically, 5 nm thick amorphous diamond-like carbon (a:C) and nitrogenated diamond-like carbon (a:CNx) overcoats were deposited by low deposition rate sputtering onto a thin film disk consisting of either CoCrPt/CrV/NiP/AlMg or CoCrPt/CrV/glass. The wear durability and frictional behavior of these hard disks were ascertained using a recently developed depth sensing reciprocating nanoscratch test. It was determined that the CN0.14/CoCrPt/CrV/glass disk exhibited the most wear resistance, least amount of plastic deformation, and lowest kinetic friction coefficient after the last wear event. Core level x-ray photoelectron spectroscopy (XPS) results of sputter cleaned overcoats indicated that nitrogen up to 14 at. % incorporated into the amorphous network resulted in these improvements near the overcoat/magnetic layer interface, since there was an increase in the number of N-sp3 C bonded sites in a predominantly N-sp2 C bonded matrix. However, nonsputter cleaned overcoats exhibited a more graphitic pyridine-like (nondoping configuration) structure near the surface as evidenced by the increase in C(Double Bond)N versus C–N bonds and the valence band XPS determined appearance of the 2p-π band near the Fermi level (EF). Therefore, XPS sputter cleaning revealed a gradient in the chemical nature of the overcoats through the thickness. In addition, micro-Raman spectroscopy established that a further increase of nitrogen (≥18 at. %) weakened the overcoat structure due to the formation of terminated sites in the amorphous carbon network, since nitrogen failed to connect the sp2 domains within the network. This, in conjunction with an increase in the intensity of the 2p-π band from the valence band XPS spectra and the increase in the G-band position and ID/IG ratio from the Raman spectra, confirmed the increase in the size and number of sp2 bonds in the CN0.18 overcoat. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.369654
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  • 7
    Electronic Resource
    Electronic Resource
    X-ray diffraction analysis of SiGe/Si heterostructures on sapphire substrates (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 924-926 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Si/Si1−xGex heterostructures on improved silicon-on-sapphire substrates were grown epitaxially by ultrahigh vacuum chemical vapor deposition for application as p-channel field effect transistors. High-resolution triple-axis x-ray diffraction was used to analyze these structures quantitatively and to evaluate their thermal stability. Outdiffusion of Ge from the strained Si1−xGex quantum well was observed after annealing at 850 °C. The amount of outdiffusion was comparable to that observed in Si1−xGex structures on bulk Si wafers. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.122039
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  • 8
    Electronic Resource
    Electronic Resource
    Atomic layer controlled growth of SiO2 films using binary reaction sequence chemistry (1997)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 70 (1997), S. 1092-1094 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: SiO2 thin films were deposited with atomic layer control using binary reaction sequence chemistry. The SiO2 growth was accomplished by separating the binary reaction SiCl4+2H2O→SiO2+4HCl into two half-reactions. Successive application of the half-reactions in an ABAB... sequence produced SiO2 deposition at temperatures between 600 and 800 K and reactant pressures of 1–10 Torr. The SiO2 growth was monitored using ellipsometry versus substrate temperature and reactant exposure time. The maximum SiO2 deposition per AB cycle was 1.1 Å/AB cycle at 600 K. The surface topography measured using atomic force microscopy was extremely flat with a roughness nearly identical to the initial substrate. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.118494
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  • 9
    Electronic Resource
    Electronic Resource
    Potentiometric imaging of (La0.7Sr0.3)MnO3 thin films (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 75 (1999), S. 1152-1154 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Scanning tunneling potentiometry has been used to simultaneously image the surface topography and map the potential distribution on films of (La0.7Sr0.3)MnO3 deposited on polycrystalline and single crystal MgO substrates. Potential steps in the polycrystalline films coincide with the crystallite boundaries in the film. The grain boundary resistivity varies in the range 3×10−7–3×10−5 Ω cm2, with a typical value of 6×10−6 Ω cm2. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.124626
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  • 10
    Electronic Resource
    Electronic Resource
    Power law wave number spectra of fractal particle distributions advected by flowing fluids (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 8 (1996), S. 2426-2434 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Recently, it has been shown that an initial cloud of particles advected by a fluid may, under common circumstances (e.g., when the particles float on the fluid surface), eventually becomes distributed on a fractal set in space. This paper considers the characterization of such fractal spatial patterns by wave number spectra. If a scaling range exists in which the spectrum has an observable power law dependence, k−ρ, then the exponent ρ is given by ρ=D2+1−M, where D2 is the correlation dimension of the fractal attractor and M is the dimension of the relevant space. We find that observability of the power law may be obscured by fluctuations in the k-spectrum, but that averaging can be employed to compensate for this. Theoretical results and supporting numerical computations utilizing a random map are presented. In the companion paper by Sommerer [Phys. Fluids 8, 2441 (1996)], an experimental example utilizing particles floating on the surface of a flowing fluid is given. (More generally we note that our result for the k-spectrum power law exponent ρ should apply to fractal patterns in other physical contexts.) © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.869026
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