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  • 1
    Electronic Resource
    Electronic Resource
    The Korteweg–de Vries–Zakharov–Kuznetsov equation for electron-acoustic waves (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 2649-2656 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Motivated by a recent paper [Phys. Plasmas 7, 2987 (2000)] highlighting the potential importance of the electron-acoustic wave in interpreting the solitary waves observed by high time resolution measurements of the electric field in the auroral region, the effect of a magnetic field on weakly nonlinear electron-acoustic waves is investigated. A Korteweg–de Vries–Zakharov–Kuznetsov (KdV-ZK) equation is derived for a plasma comprised of cool and hot electrons and a species of fluid ions. Two models are employed for the ions: magnetized and unmagnetized. When the ions are magnetized the frequency constraints imposed upon the electron-acoustic wave packet prove to be too limiting to be of general use. The second model, which treats the ions as a stationary neutralizing background, overcomes the restrictions imposed by the former and is more fitting for the frequency domain of the electron-acoustic wave. Plane and ellipsoidal soliton solutions are admitted by the KdV-ZK equation, the latter perhaps able to explain some of the two dimensional features of the solitary waves observed in the Earth's high altitude auroral region. Both models for the ions predict only negative potential solitons. It is discussed how the plasma model might be adapted to produce positive potential solitons. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1363665
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  • 2
    Electronic Resource
    Electronic Resource
    The electron-acoustic mode in a plasma with hot suprathermal and cool Maxwellian electrons (1999)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 6 (1999), S. 44-49 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The electron-acoustic wave, in a plasma with hot suprathermal, kappa-distributed electrons and cool, Maxwellian electrons, is investigated. This model is a generalization of those that have been investigated previously, and through its parametrization by κ, can be reduced to many previous models of the stable wave. It is found that the hot suprathermal electrons significantly increase the Landau damping of the wave at small wave numbers, i.e., in its acoustic regime. Results from a survey of parameter space, which help to identify parameters for which the stable mode will be only weakly Landau damped, are presented. The dependence of the Landau damping on the fraction of suprathermal electrons, which is related to the index, κ, of the hot electron distribution, is investigated in detail. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873256
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  • 3
    Electronic Resource
    Electronic Resource
    A dispersion function for plasmas containing superthermal particles (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 2098-2109 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: It is now well known that space plasmas frequently contain particle components that exhibit high, or superthermal, energy tails with approximate power law distributions in velocity space. Such nonthermal distributions, with overabundances of fast particles, can be better fitted, for supra- and superthermal velocities, by generalized Lorentzian or kappa distributions, than by Maxwellians or one of their variants. Employing the kappa distribution, with real values of the spectral index κ, in place of the Maxwellian we introduce a new plasma dispersion function expected to be of significant importance in kinetic theoretical studies of waves in space plasmas. It is demonstrated that this function is proportional to Gauss' hypergeometric function 2F1[1,2κ+2;κ+2;z] enabling the well-established theory of the hypergeometric function to be used to manipulate dispersion relations. The reduction, for integer values of κ, to the less general so-called modified plasma dispersion function [Phys. Fluids B 3, 1835 (1991)] is demonstrated. An example illustrating the use of the function is presented. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871296
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  • 4
    Electronic Resource
    Electronic Resource
    Ballistic transport in one-dimensional constrictions formed in deep two-dimensional electron gases (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 67 (1995), S. 109-111 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We show that small structures can be defined in high mobility two-dimensional electron gases formed at a depth of 2770 A(ring) below the surface in GaAs/Al0.33Ga0.67As heterostructures. The differential conductance of one-dimensional constrictions defined by split gates in such deep electron gases showed more than 20 quantised plateaus. The absence of resonant structures on the plateaus demonstrates the absence of potential fluctuations in the constrictions. By applying a dc source-drain bias we have measured the energy spacings of the first 18 subbands, and the effect of a small perpendicular magnetic field on the energy spacings has been investigated. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.115498
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  • 5
    Electronic Resource
    Electronic Resource
    Aharonov–Bohm effect and one-dimensional ballistic transport through two independent parallel channels (1993)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 63 (1993), S. 3191-3193 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have developed a new technique to contact a submicrometer metal dot gate independently of surrounding gates. With this we have made two ballistic channels in parallel on a GaAs-AlGaAs heterostructure. Independent control over all the gates allows unprecedented flexibility to adjust both the size of the dot and the widths of the channels. In a perpendicular magnetic field we can obtain extremely large Aharonov–Bohm oscillations and a double-frequency oscillation indicative of edge state charging in an open system. At low magnetic fields we see no evidence for any interaction between the one-dimensional subbands in the two channels.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.110195
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  • 6
    Electronic Resource
    Electronic Resource
    Tunneling between totally quantized levels in GaAs/AlGaAs asymmetric triple-barrier heterostructures in high magnetic fields (1991)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 59 (1991), S. 803-805 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Electron transport is studied in GaAs/AlGaAs asymmetric triple-barrier resonant tunneling structures in a high magnetic field perpendicular to the interfaces. Besides the resonance peaks arising from tunneling between two quantum wells, a series of fine structure is observed in the valley region of the current-voltage characteristics, which is attributed to electron transitions between well defined totally quantized levels (Landau levels) in the two wells, together with the emission of a longitudinal optical phonon. In the voltage region of the main current peak, any structures which shift with magnetic field are not observed, suggesting that the tunneling in this bias region is mainly determined by Δn=0 elastic transitions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.105348
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  • 7
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    One-dimensional particle-in-cell simulations of electrostatic Bernstein waves in plasmas with kappa velocity distributions (2015)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2015-10-14
    Description: Electrostatic Bernstein waves that propagate exactly perpendicularly to a static magnetic field in an electron-ion plasma are investigated using one-and-two-halves dimensional particle-in-cell simulations. An ion-to-electron mass ratio of m i / m e  = 100 is used, allowing sufficient separation of the electron and ion time scales while still accounting for the ion dynamics without resorting to exceptionally long simulation run times. As a consequence of the mass ratio used, both the high frequency electron Bernstein wave and the lower frequency ion Bernstein wave are resolved within a single simulation run. The simulations presented here use isotropic three-dimensional kappa velocity distributions as well as the widely used Maxwellian velocity distribution, and the results from using each of these velocity distributions are analysed and compared. The behaviour of the Bernstein waves is found to be significantly dependent on the spectral index, κ , of the kappa distribution in all frequency domains of the Bernstein waves. In both the Maxwellian and kappa cases, spectral analysis of the electric field (wave) intensities, as a function of ω and k , show very good agreement between the simulation results and the linear dispersion relation for Bernstein waves. This agreement serves to validate the simulation techniques used, as well as the theory of Bernstein waves in plasmas with a kappa velocity distribution. The intensity of the field fluctuations in the simulations containing an abundance of superthermal particles, i.e., where the plasma has a kappa velocity distribution with a low kappa index, is slightly higher compared to the simulations of plasmas with higher kappa values. The plasmas with low kappa values also exhibit a broader region in frequency space of high intensity field fluctuations.
    Print ISSN: 1070-664X
    Electronic ISSN: 1089-7674
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 8
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    Atomically layer-by-layer diffusion of oxygen/hydrogen in highly epitaxial PrBaCo2O5.5+δ thin films (2015)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2015-12-15
    Description: Single-crystalline epitaxial thin films of PrBaCo 2 O 5.5+δ (PrBCO) were prepared, and their resistance R(t) under a switching flow of oxidizing and reducing gases were measured as a function of the gas flow time t in the temperature range of 200–800 °C. During the oxidation cycle under O 2 , the PrBCO films exhibit fast oscillations in their dR(t)/dt vs. t plots, which reflect the oxidation processes, Co 2+ /Co 3+ → Co 3+ and Co 3+ → Co 3+ /Co 4+ , that the Co atoms of PrBCO undergo. Each oscillation consists of two peaks, with larger and smaller peaks representing the oxygen/hydrogen diffusion through the (BaO)(CoO 2 )(PrO)(CoO 2 ) layers of PrBCO via the oxygen-vacancy-exchange mechanism. This finding paves a significant avenue for cathode materials operating in low-temperature solid-oxide-fuel-cell devices and for chemical sensors with wide range of operating temperature.
    Print ISSN: 0003-6951
    Electronic ISSN: 1077-3118
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 9
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    Stopbands in the existence domains of acoustic solitons (2014)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2014-10-02
    Description: A fully nonlinear Sagdeev pseudopotential approach is used to study the existence domain of fast mode ion-acoustic solitons in a three-species plasma composed of cold and warm adiabatic positive ion species and Boltzmann electrons. It is shown that for appropriate values of the cold-to-warm ion charge-to-mass ratio, μ , and the effective warm ion-to-electron temperature ratio, τ , there is a range in cold to warm ion charge density ratio, f , over which a stopband in soliton speed exists. Solitons do not propagate in the stopband, although they can occur for both higher and lower speeds. The stopbands are associated with a limiting curve of the existence domain that is double-valued in speed for a range of values of f . Analytical estimates of the upper and lower limits of τ and μ that support stopbands are found. It is suggested that, inter alia , the analysis should be applicable to the solar wind plasma.
    Print ISSN: 1070-664X
    Electronic ISSN: 1089-7674
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 10
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    Internal resonance with commensurability induced by an auxiliary oscillator for broadband energy harvesting (2016)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2016-05-17
    Description: An internal resonance based broadband vibration energy harvester is proposed by introducing an auxiliary oscillator to the main nonlinear harvesting oscillator. Compared to conventional nonlinear energy harvesters, the natural frequencies of this two-degree-of-freedom nonlinear system can be easily adjusted to be commensurable which will result in more resonant peaks and better wideband performance. Experimental measurements and equivalent circuit simulations demonstrate that this design outperforms its linear counterpart. In addition to the open-circuit voltage, the optimal resistance to obtain the maximum power is determined. Nearly 130% increase in the bandwidth is achieved compared to the linear counterpart at an excitation level of 2 m/s 2 . The findings provide insight for the design of a broadband energy harvester when there is nonlinearity and internal resonance.
    Print ISSN: 0003-6951
    Electronic ISSN: 1077-3118
    Topics: Physics
    Published by American Institute of Physics (AIP)
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