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  • Articles  (56)
  • American Institute of Physics (AIP)  (53)
  • Wiley-Blackwell
  • 2000-2004  (56)
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  • Articles  (56)
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  • 1
    Electronic Resource
    Electronic Resource
    Transverse demagnetizing factors of long rectangular bars. II. Numerical calculations for arbitrary susceptibility (2002)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 91 (2002), S. 5260-5267 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: For an infinitely long bar with rectangular cross section 2a×2b and constant susceptibility χ in a uniform transverse applied field Ha along dimension a, the fluxmetric and magnetometric demagnetizing factors Nf,m as functions of a/b and χ are accurately computed using a finite-elements method. By comparison of the computed results with exact analytical results for χ=−1,0,∞ and with a set of conjugate relations derived in this work, the elements distributions have been optimized to give a minimum discretization error. This error is further greatly reduced in the final results of Nf,m by using an error correction approach previously proposed in a similar work for cylinders. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1459746
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  • 2
    Electronic Resource
    Electronic Resource
    General solution for the thermal wave scattering in fiber composites (2002)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 91 (2002), S. 1087-1098 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this article we present a general solution for the ac temperature field generated from a modulated heating in an opaque material containing a series of aligned subsurface cylinders. The model includes the multiple scattering effects suffered by the plane thermal wave, generated by a planar heat source, when interacting with the cylinders and with the sample surfaces. A series solution to the heat diffusion equation and a matrix formulation to solve the scattering coefficients are used. There are no restrictions on the cylinders number, on their size and position inside the material, nor on the thermal properties of cylinders and sample. For completeness the case of coated cylinders is also investigated. Numerical calculations for the case of nonconducting cylinders illustrate the effect of the multiple scattering of the incident thermal wave on the sample surface temperature. A specific case of interest of the model is its application to the thermal characterization and nondestructive evaluation of fiber reinforced composites. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1421633
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  • 3
    Electronic Resource
    Electronic Resource
    Determination of the glass transition and nucleation temperatures in Ge2Sb2Te5 sputtered films (2002)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 91 (2002), S. 697-702 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Amorphous Ge2Sb2Te5 films were prepared by rf sputtering from the bulk alloy. Their electrical and optical properties were analyzed using impedance and optical transmission measurements as a function of temperature. From this analysis, it is found that the glass transition temperature of the as-prepared amorphous films is of about 100 °C. This result is confirmed by calorimetric measurements. Impedance and optical measurements in films measured at temperatures between the glass transition and the crystallization temperatures show the appearance of the nucleation centers. Using models for two-phase materials, the electrical parameters of the crystalline and amorphous phases were estimated and related with structural parameters of the samples. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1427146
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  • 4
    Electronic Resource
    Electronic Resource
    Bonding structure in amorphous carbon nitride: A spectroscopic and nuclear magnetic resonance study (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 90 (2001), S. 675-681 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Since the prediction of Liu and Cohen [Science 245, 841 (1989)] of the potential extraordinary mechanical properties of crystalline β-C3N4, many authors have attempted its synthesis. However, in most cases, the obtained materials are amorphous phases with a complex bonding structure. Their characterization is complicated due to the absence of a reference compound, the lack of long-range order, and the poor knowledge about their bonding structure. In this article, we present 1H, 13C, and 15N solid-state nuclear magnetic resonance (NMR) measurements for the determination of the bonding types in amorphous CNx films. NMR measurements do not require long-range order and are able to clearly identify the signals from the sp2- and sp3-bonded phases. The analysis of the data obtained by other characterization techniques, such as infrared spectroscopy, x-ray photoelectron spectroscopy, electron energy-loss spectroscopy, and x-ray absorption near-edge spectroscopy on the same sample, based on the information acquired by NMR, enables the description of a structure model for the studied amorphous-CNx phase prepared by dc-magnetron sputtering and to revise the interpretation found in the literature. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1380998
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  • 5
    Electronic Resource
    Electronic Resource
    Analysis and modeling of AlxGa1−xN-based Schottky barrier photodiodes (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 2081-2091 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Schottky barrier photovoltaic detectors have been fabricated on n-AlxGa1−xN(0≤x≤0.35) and p-GaN epitaxial layers grown on sapphire. Their characteristics have been analyzed and modeled, in order to determine the physical mechanisms that limit their performance. The influence of material properties on device parameters is discussed. Our analysis considers front and back illumination and distinguishes between devices fabricated on ideal high-quality material and state-of-the-art heteroepitaxial AlxGa1−xN. In the former case, low doping levels are advisable to achieve high responsivity and a sharp spectral cutoff. The epitaxial layer should be thin (〈0.5 μm) to optimize the ultraviolet/visible contrast. In present devices fabricated on heteroepitaxial AlxGa1−xN, the responsivity is limited by the diffusion length. In this case, thick AlxGa1−xN layers are advisable, because the reduction in the dislocation density results in lower leakage currents, larger diffusion length, and higher responsivity. In order to improve bandwidth and responsivity, and to achieve good ohmic contacts, a moderate n-type doping level (∼1018 cm−3) is recommended. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1305838
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  • 6
    Electronic Resource
    Electronic Resource
    Predictions on runaway current and energy during disruptions in tokamak plasmas (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 3369-3377 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A simple model for a tokamak disruption, taking into account the replacement of the plasma current by the runaway current, is used to evaluate the generation and energy of the runaway population during the current quench phase of a fast disruptive event. The potential efficiency of the ripple resonance and the magnetic fluctuations for runaway current mitigation during plasma disruptions, as well as their dependence on the runaway generation mechanism, are discussed. Predictions are made for the Joint European Torus (JET) [Nucl. Fusion 25, 1011 (1985)] and the projected International Thermonuclear Experimental Reactor (ITER) [ITER EDA Agreement and Protocol 2, International Atomic Energy Agency, Vienna, 1994]. It is shown that the ripple resonance leads to a reduction in the runaway beam energy if the runaway production is dominated by the Dreicer generation process; however, the effect will be negligible if the secondary generation mechanism is included. The effect of anomalous radial runaway losses induced by enhanced magnetic fluctuations is stronger. Large enough levels of magnetic fluctuations, leading to runaway electron loss rates in excess of 103 s−1, can efficiently limit the number and energy of the runaway electrons. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.874201
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  • 7
    Electronic Resource
    Electronic Resource
    On the effect of synchrotron radiation and magnetic fluctuations on the avalanche runaway growth rate (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 3814-3817 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The avalanche runaway growth rate was recently determined by analysis of the trajectories of the secondary runaway electrons in momentum space [Parks et al., Phys. Plasmas 6, 2523 (1999)]. Here, such an approach is used to study the effect of the electron synchrotron radiation and the magnetic fluctuations on the secondary generation of runaway electrons. It is found that not only the threshold electric field for runaway generation is increased due to these effects, but also the creation rate of secondary runaway electrons may be noticeably reduced for electric fields close to the threshold field. It has been shown that avalanche runaway generation can be efficiently suppressed in large tokamaks, even during major disruptions, for stochastic magnetic fluctuation levels b˜〉10−3. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1287215
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  • 8
    Electronic Resource
    Electronic Resource
    Turbulence and beam size effects on reflectometry measurements (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 2657-2665 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A two-dimensional code based on the WKB (Wenzel–Kramers–Brillouin) approximation is used to simulate reflectometry measurements in plasmas with turbulence. In this work we aim to understand, first the role of turbulence in the determination of density profiles with reflectometry and, second, the ability of reflectometry techniques to give reliable information on the characteristics of the turbulence itself. The effects on the profile determination of a rotating turbulence structure with nonperpendicular reflection are analyzed. The influence of the turbulence level, fluctuation wavelengths and antenna beam size on the density profile determination has been studied in static plasma with perpendicular launching. The code has been used to simulate correlation measurements. The results show the correlation of the reflectometry signals for different turbulence parameters. Errors in the correlation length increase when two-dimensional effects become important, though the homodyne signal works better than the phase. The correlation simulations also show the way for new methods to determine the group delay and therefore the density profile. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1368142
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  • 9
    Electronic Resource
    Electronic Resource
    Interaction of runaway electrons with lower hybrid waves via anomalous Doppler broadening (2002)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 9 (2002), S. 1667-1675 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Due to the relativistic decrease of the electron cyclotron frequency, a cyclotron resonance may appear between runaway electrons and lower hybrid waves. A single particle description of the runaway dynamics [J. R. Martín-Solís et al., Phys. Plasmas 5, 2370 (1998)] is extended to analyze the effect of the interaction of runaway electrons with lower hybrid waves via anomalous Doppler broadening. The conditions under which the resonant interaction can play a role in limiting the runaway energy are established and it is shown that, under typical lower hybrid current drive operation parameters, an efficient wave-particle coupling may occur. Observations of a fast pitch angle scattering event during the current decay phase of Ohmic discharges in the Toroidal Experiment for Technically Oriented Research (TEXTOR) [R. J. E. Jaspers, Ph.D. thesis, Technical University Eindhoven (1995)] are interpreted in terms of such interaction. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1470165
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  • 10
    Electronic Resource
    Electronic Resource
    Statistical characterization of fluctuation wave forms in the boundary region of fusion and nonfusion plasmas (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 1408-1416 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The statistical properties of plasma fluctuations have been investigated in the plasma boundary region of fusion (tokamaks and stellarators) and nonfusion plasmas. Fluctuations in ion saturation current and floating potential have a near-Gaussian character in the proximity of the velocity shear layer (rsh). However, fluctuations deviate from a Gaussian distribution when moving inside of the plasma edge (r〈rsh) or into the scrape-off layer region (r〉rsh). Furthermore, fluctuations show sporadic pulses that are asymmetric in time. The present analysis shows a coupling of those pulses and the averaged flow in the shear layer region. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873958
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